Fair Value (Reconciliation of Assets Measured at Fair Value on a Recurring Basis Using Level 3 Inputs) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 349	$ 432	$ 366
Purchases	127	88	101
Sales	(17)	(171)	(3)
Settlements	(32)	(20)	(12)
Net unrealized (losses) gains in accumulated other comprehensive income	(4)	9	7
Net realized (losses) gains in investment and other income	(6)	11	(27)
Balance at end of period	417	349	432
Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	141	120	62
Purchases	92	43	76
Sales	0	(4)	0
Settlements	(25)	(20)	(12)
Net unrealized (losses) gains in accumulated other comprehensive income	0	0	0
Net realized (losses) gains in investment and other income	0	2	(6)
Balance at end of period	208	141	120
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	208	312	304
Purchases	35	45	25
Sales	(17)	(167)	(3)
Settlements	(7)	0	0
Net unrealized (losses) gains in accumulated other comprehensive income	(4)	9	7
Net realized (losses) gains in investment and other income	(6)	9	(21)
Balance at end of period	$ 209	$ 208	$ 312