Investment Securities (Investment) (Details) (USD $) In Millions, unless otherwise specified	Mar. 31, 2014	Dec. 31, 2013
Investment [Line Items]
Investments	$ 45,450	$ 43,662
Domestic Corporate Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	19,711	19,600
Debt securities, Gross unrealized gains	3,088	2,323
Debt securities, Gross unrealized losses	(138)	(217)
Domestic Corporate Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	22,661	21,706
US States and Political Subdivisions Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	5,115	4,245
Debt securities, Gross unrealized gains	409	235
Debt securities, Gross unrealized losses	(130)	(191)
US States and Political Subdivisions Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	5,394	4,289
Commercial Mortgage Backed Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	2,986	2,929
Debt securities, Gross unrealized gains	198	188
Debt securities, Gross unrealized losses	(61)	(82)
Commercial Mortgage Backed Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	3,123	3,035
Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	1,770	1,819
Debt securities, Gross unrealized gains	143	139
Debt securities, Gross unrealized losses	(39)	(48)
Residential Mortgage Backed Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	1,874	1,910
Asset-backed Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	7,347	7,373
Debt securities, Gross unrealized gains	32	60
Debt securities, Gross unrealized losses	(41)	(46)
Asset-backed Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	7,338	7,387
Foreign Corporate Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	1,716	1,741
Debt securities, Gross unrealized gains	137	103
Debt securities, Gross unrealized losses	(64)	(86)
Foreign Corporate Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	1,789	1,758
Foreign Government Debt Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	2,058	2,336
Debt securities, Gross unrealized gains	103	81
Debt securities, Gross unrealized losses	(3)	(7)
Foreign Government Debt Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	2,158	2,410
US Treasury and Government [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	707	752
Debt securities, Gross unrealized gains	48	45
Debt securities, Gross unrealized losses	(18)	(27)
US Treasury and Government [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Debt securities, Estimated fair value	737	770
Retained Interest [Member]
Investment [Line Items]
Retained interests and AFS securities, Amortized cost	64	64
Retained interests, Gross unrealized gain	11	8
Retained interests, Gross unrealized loss	0	0
Retained Interest [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Retained interests, Estimated fair value	75	72
Available-for-sale Securities [Member]
Investment [Line Items]
Debt and AFS securities, Amortized cost	195	203
Retained interests, Gross unrealized gain	46	51
Available-for-sale Equity Securities, Gross Unrealized Loss	(8)	(3)
Available-for-sale securities, Equity, Estimated fair value	233
Available-for-sale Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Available-for-sale securities, Equity, Estimated fair value		251
Trading Securities [Member]
Investment [Line Items]
Trading Securities, Unrealized Holding Gain	0	0
Trading Securities, Unrealized Holding Loss	0	0
Trading Securities [Member] | Amortized Cost [Member]
Investment [Line Items]
Trading Securities	68	74
Trading Securities [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Trading Securities	68	74
Total [Member]
Investment [Line Items]
Retained interests, Gross unrealized gain	4,215	3,233
Retained interests, Gross unrealized loss	(502)	(707)
Total [Member] | Amortized Cost [Member]
Investment [Line Items]
Marketable Securities	41,737	41,136
Total [Member] | Estimated Fair Value [Member]
Investment [Line Items]
Marketable Securities	45,450	43,662
Mortgage-backed Securities, Issued by Private Enterprises [Member] | Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Debt securities, Estimated fair value	649
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Residential Mortgage Backed Securities [Member]
Investment [Line Items]
Debt securities, Estimated fair value	$ 1,225