Derivative Financial Instruments - Schedule of Derivative Instruments (Details) (USD $) In Millions, unless otherwise specified	Jun. 30, 2013	Dec. 31, 2012
Derivative Asset [Abstract]
Derivatives accounted for as fair value hedges	$ 0	$ 7
Derivatives accounted for as cash flow hedges	263	506
Derivatives not designated as hedging instruments	23	23
Total Derivative Financial Assets	1,132	1,683
Less: Gross amounts offset in the balance sheet	1,132	1,683
Net amounts of derivative financial assets and liabilities presented in the balance sheet	0	0
Less: Gross amounts of cash or financial instrument collateral received/posted not subject to an enforceable master netting agreement	0	0
Net amounts of derivative financial assets and liabilities	0	0
Derivative Liability [Abstract]
Derivatives accounted for as fair value hedges	0	0
Derivatives accounted for as cash flow hedges	(264)	(512)
Derivatives not designated as hedging instruments	(298)	(1,118)
Total Derivative Financial Liabilities	562	1,630
Less: Gross amounts offset in the balance sheet	(559)	(1,608)
Net amounts of derivative financial assets and liabilities presented in the balance sheet	3	22
Less: Gross amounts of cash or financial instrument collateral received/posted not subject to an enforceable master netting agreement	0	0
Net amounts of derivative financial assets and liabilities	3	22
Debt [Member]
Derivative Asset [Abstract]
Derivatives not designated as hedging instruments	846	1,147
Derivative Liability [Abstract]
Derivatives not designated as hedging instruments	0	0
Interest rate swaps [Member]
Derivative Asset [Abstract]
Derivatives accounted for as fair value hedges	0	7
Derivatives accounted for as cash flow hedges	19	24
Derivatives not designated as hedging instruments	23	23
Derivative Liability [Abstract]
Derivatives accounted for as fair value hedges	0	0
Derivatives accounted for as cash flow hedges	(190)	(474)
Derivatives not designated as hedging instruments	(276)	(1,111)
Interest rate swaps [Member] | Debt [Member]
Derivative Asset [Abstract]
Derivatives not designated as hedging instruments	349	469
Derivative Liability [Abstract]
Derivatives not designated as hedging instruments	0	0
Currency swaps [Member]
Derivative Asset [Abstract]
Derivatives accounted for as fair value hedges	0	0
Derivatives accounted for as cash flow hedges	244	482
Derivatives not designated as hedging instruments	0	0
Derivative Liability [Abstract]
Derivatives accounted for as fair value hedges	0	0
Derivatives accounted for as cash flow hedges	(74)	(38)
Derivatives not designated as hedging instruments	(22)	(7)
Currency swaps [Member] | Debt [Member]
Derivative Asset [Abstract]
Derivatives not designated as hedging instruments	497	678
Derivative Liability [Abstract]
Derivatives not designated as hedging instruments	$ 0	$ 0