Investment Securities (Investment) (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 42,857	$ 41,136
Gross unrealized gain	5,319	3,233
Gross unrealized losses	(349)	(707)
Estimated fair value	47,827us-gaap_AvailableForSaleSecurities	43,662us-gaap_AvailableForSaleSecurities
Investments	47,827us-gaap_Investments	43,662us-gaap_Investments
US Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19,889	19,600
Gross unrealized gain	3,967	2,323
Gross unrealized losses	(69)	(217)
Estimated fair value	23,787	21,706
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	5,181	4,245
Gross unrealized gain	624	235
Gross unrealized losses	(56)	(191)
Estimated fair value	5,749	4,289
Residential Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,578	1,819
Gross unrealized gain	153	139
Gross unrealized losses	(6)	(48)
Estimated fair value	1,725	1,910
Commercial mortgage backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,903	2,929
Gross unrealized gain	170	188
Gross unrealized losses	(10)	(82)
Estimated fair value	3,063	3,035
Asset-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	8,084	7,373
Gross unrealized gain	9	60
Gross unrealized losses	(175)	(46)
Estimated fair value	7,918	7,387
Corporate non US
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,380	1,741
Gross unrealized gain	126	103
Gross unrealized losses	(30)	(86)
Estimated fair value	1,476	1,758
Government - non-U.S.
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,646	2,336
Gross unrealized gain	152	81
Gross unrealized losses	(2)	(7)
Estimated fair value	1,796	2,410
U.S. Government and federal agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,957	752
Gross unrealized gain	56	45
Gross unrealized losses	0	(27)
Estimated fair value	2,013	770
Retained Interest [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	20	64
Gross unrealized gain	4	8
Gross unrealized losses	0	0
Estimated fair value	24	72
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	197	203
Gross unrealized gain	58	51
Gross unrealized losses	(1)	(3)
Estimated fair value	254	251
Trading Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	22	74
Gross unrealized gain	0	0
Gross unrealized losses	0	0
Estimated fair value	22	74
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments	534
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments	$ 1,191

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

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