Fair Value Measurements (Quantitative Information About Level 3 Measurements) (Details) (Fair Value, Measurements, Recurring [Member], USD $) In Millions, unless otherwise specified							6 Months Ended					6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011	Jun. 30, 2012 Fair Value, Inputs, Level 3 [Member]	Dec. 31, 2011 Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2012 State And Municipal Securities [Member] Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2012 State And Municipal Securities [Member] Minimum [Member] Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2012 State And Municipal Securities [Member] Maximum [Member] Fair Value, Inputs, Level 3 [Member]		Jun. 30, 2012 Auction-Rate Preferred Securities [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2012 Auction-Rate Preferred Securities [Member] Minimum [Member] Fair Value, Inputs, Level 3 [Member]	Jun. 30, 2012 Auction-Rate Preferred Securities [Member] Maximum [Member] Fair Value, Inputs, Level 3 [Member]
Fair Value Inputs, Assets, Quantitative Information [Line Items]
Total assets at fair value	$ 10,895	$ 10,979	$ 243	$ 436	$ 24	[1]					$ 215
Unobservable Input, Discount rate							6.00%	[1]	9.00%	[1]		3.00%	7.00%
Unobservable Input, Workout period							4 years	[1]	5 years	[1]		2 years	5 years

[1] Primarily auction-rate securities.