Benefit Plans (Activity of plan assets with significant unobservable fair value inputs) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2011		Dec. 31, 2010		Dec. 31, 2009
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, December 31,	$ 2,462	[1]	$ 2,476	[2]
Alternative Investments [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1,	124		92		90
Actual return on plan assets	9		9		12
Purchases, sales and settlements			23	[3]	(10)
Transfers in/out of Level 3					0
Sales	(55)
Purchases	21	[3]
Fair value of plan assets, December 31,	99		124		92
Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets, January 1,	0		0		61
Actual return on plan assets	0		0		(12)
Purchases, sales and settlements			0		0
Transfers in/out of Level 3					(49)
Sales	0
Purchases	0
Fair value of plan assets, December 31,	$ 0		$ 0		$ 0

[1] The total fair value of plan assets excludes $16 million of accrued income at December 31, 2011.

[2] The total fair value of plan assets excludes $8 million of accrued income at December 31, 2010.

[3] The net purchases in alternative investments during 2011 and 2010 relates to investment commitments that existed prior to January 1, 2009.