| Date | Acquired | Amount |
|---|---|---|
| May 21, 2018 | $ 1,680,000,000 | |
| Oct 18, 2017 | Undisclosed amount | |
| Nov 10, 2016 | $ 540,000,000 | |
| May 03, 2016 | Undisclosed amount | |
| Nov 05, 2015 | Undisclosed amount | |
| Jun 01, 2015 | Undisclosed amount | |
| Dec 11, 2014 | $ 800,000,000 | |
| Sep 22, 2014 | Undisclosed amount | |
| Jun 27, 2013 | $ 600,000,000 | |
| May 28, 2013 | Undisclosed amount | |
| May 22, 2013 | Undisclosed amount | |
| Dec 20, 2012 | $ 150,000,000 | |
| Nov 30, 2011 | $ 400,000,000 | |
| Nov 01, 2011 | $ 120,000,000 | |
| Oct 03, 2011 | Undisclosed amount | |
| Oct 03, 2011 | Undisclosed amount | |
| Sep 07, 2011 | Undisclosed amount | |
| Jul 18, 2011 | Undisclosed amount | |
| Jan 18, 2011 | $ 109,000,000 | |
| Jul 28, 2010 | $ 240,000,000 | |
| Sep 15, 2009 | $ 1,800,000,000 | |
| Aug 31, 2009 | Undisclosed amount | |
| Sep 30, 2007 | Undisclosed amount | |
| May 03, 2007 | Undisclosed amount | |
| Dec 13, 2006 | Undisclosed amount | |
| Oct 20, 2006 | Undisclosed amount | |
| Oct 01, 2006 | Undisclosed amount | |
| Sep 05, 2006 | Undisclosed amount | |
| Jun 26, 2006 | Undisclosed amount | |
| Apr 21, 2006 | Undisclosed amount | |
| Dec 16, 2005 | Undisclosed amount | |
| Dec 03, 2005 | $ 3,400,000,000 | |
| Dec 07, 2004 | Undisclosed amount | |
| May 07, 2004 | Undisclosed amount | |
| May 19, 2003 | Undisclosed amount | |
| Apr 15, 2002 | Undisclosed amount | |
| Dec 05, 2001 | Undisclosed amount | |
| Jan 04, 1999 | Undisclosed amount | |
| Sep 16, 1997 | Undisclosed amount | |
| Sep 05, 1997 | Undisclosed amount | |
| Mar 14, 1997 | Undisclosed amount | |
| May 20, 1996 | Undisclosed amount | |
| Oct 30, 1995 | $ 500,000,000 | |
| Jan 01, 1995 | Undisclosed amount | |
| Aug 31, 1994 | Undisclosed amount | |
| Jun 29, 1992 | Undisclosed amount | |
| Jun 21, 1990 | Undisclosed amount | |
| Mar 26, 1990 | Undisclosed amount |