Derivative and Other Hedging Instruments (Remaining Interest Rate Swap Term) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended							12 Months Ended
	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Unrealized (loss) gain on derivative instruments, net	$ 51	$ 52	$ 52	$ 54	$ (513)	$ (252)	$ 61	$ 205	$ (650)	$ (24)
Notional Amount				0					0	6,450	2,050
Notional amount of forward starting swaps				(103)				12,477	(103)
Remaining interest rate swap term, maximum								4 months	5 months
Not Designated as Hedging Instrument [Member]
Notional Amount				30,250				46,850	30,250
Average Maturity (Years)								4 years 4 months 10 days	3 years 6 months
Average Fixed Pay Rate				1.57%				1.46%	1.57%
Average Receive Rate				0.35%				0.29%	0.35%
Net Estimated Fair Value				(782)				(1,229)	(782)
Greater Than One Year and Less Than or Equal to Three Years [Member]
Notional Amount				11,350				14,600	11,350
Average Maturity (Years)								2 years	2 years 1 month 6 days
Average Fixed Pay Rate				1.22%				1.23%	1.22%
Average Receive Rate				0.30%				0.26%	0.30%
Net Estimated Fair Value				(148)				(294)	(148)
Greater Than Three Years and Less Than or Equal to Five Years [Member]
Notional Amount				16,700				20,250	16,700
Average Maturity (Years)								4 years 1 month 12 days	3 years 10 months 24 days
Average Fixed Pay Rate				1.77%				1.48%	1.77%
Average Receive Rate				0.35%				0.29%	0.35%
Net Estimated Fair Value				(607)				(666)	(607)
Greater Than Five Years and Less than or Equal to Seven Years [Member]
Notional Amount				950				5,600	950
Average Maturity (Years)								6 years 1 month 6 days	5 years 8 months 12 days
Average Fixed Pay Rate				1.56%				1.53%	1.56%
Average Receive Rate				0.57%				0.34%	0.57%
Net Estimated Fair Value				(9)				(163)	(9)
Greater Than Seven Years and Less than or Equal to Ten Years [Member]
Notional Amount				1,250				5,200	1,250
Average Maturity (Years)								9 years 2 months 10 days	8 years 2 months 12 days
Average Fixed Pay Rate				1.99%				1.89%	1.99%
Average Receive Rate				0.55%				0.35%	0.55%
Net Estimated Fair Value				(18)				(113)	(18)
Greater Than Ten Years [Member]
Notional Amount								1,200
Average Maturity (Years)								10 years 2 months 10 days
Average Fixed Pay Rate								1.79%
Average Receive Rate								0.31%
Net Estimated Fair Value								7
Interest Rate Swap [Member]
Average Maturity (Years)								10 years
Interest Rate Swap [Member]
Notional amount of forward starting swaps				$ 2,600				$ 1,700	$ 2,600