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	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	$ 235	$ 362	$ 417	$ 349
Purchases	2	6	53	46
Sales	(11)	(2)	(20)	(16)
Settlements	(1)	(13)	(1)	(23)
Net unrealized losses in accumulated other comprehensive income	(9)	0	(12)	(3)
Net realized gains in investment and other income	8	(5)	9	(5)
Transfers to held-to-maturity	0		(222)
Balance at end of period	224	348	224	348
Debt Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	7	140	208	141
Purchases	0	6	0	15
Sales	0	0	0	0
Settlements	(1)	(7)	(1)	(17)
Net unrealized losses in accumulated other comprehensive income	0	0	0	0
Net realized gains in investment and other income	0	0	0	0
Transfers to held-to-maturity	0		(201)
Balance at end of period	6	139	6	139
Equity Securities [Member]
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance at beginning of period	228	222	209	208
Purchases	2	0	53	31
Sales	(11)	(2)	(20)	(16)
Settlements	0	(6)	0	(6)
Net unrealized losses in accumulated other comprehensive income	(9)	0	(12)	(3)
Net realized gains in investment and other income	8	(5)	9	(5)
Transfers to held-to-maturity	0		(21)
Balance at end of period	$ 218	$ 209	$ 218	$ 209