Common Share Repurchases (Details) (USD $)	1 Months Ended		6 Months Ended
	Jun. 30, 2011	May 31, 2010	Jun. 30, 2011	Jun. 30, 2010
Common Share Repurchases:
Repurchase of common shares			$ 780,000,000	$ 236,000,000
Restricted shares forfeited, recorded as treasury shares (in shares)			100,000	100,000
Number of shares reacquired through surrender of restricted shares (in shares)			400,000	400,000
Value of shares reacquired through surrender of restricted shares			19,000,000	16,000,000
Treasury shares reissued for restricted stock award grants (in shares)			1,700,000
Open Market Share Repurchases
Common Share Repurchases:
Maximum expenditure for repurchase of common stock through the date of its 2012 annual meeting	2,000,000,000	1,500,000,000
Repurchase of common shares (in shares)			12,500,000	5,700,000
Repurchase of common shares			761,000,000	220,000,000
Remaining balance under stock repurchase authorization	$ 2,200,000,000		$ 2,200,000,000