Investment Securities (Investment) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended	12 Months Ended
Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	$ 36,242	$ 42,493
Gross unrealized gain	5,742	5,305
Gross unrealized losses	(131)	(320)
Estimated fair value	41,853us-gaap_AvailableForSaleSecurities	47,478us-gaap_AvailableForSaleSecurities
Investments	41,853us-gaap_Investments	47,478us-gaap_Investments
US Corporate
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	20,015	19,889
Gross unrealized gain	4,322	3,967
Gross unrealized losses	(52)	(69)
Estimated fair value	24,285	23,787
State and municipal
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	4,967	5,181
Gross unrealized gain	667	624
Gross unrealized losses	(50)	(56)
Estimated fair value	5,584	5,749
Residential Mortgage Backed Securities
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,129	1,578
Gross unrealized gain	100	153
Gross unrealized losses	(4)	(6)
Estimated fair value	1,225	1,725
Commercial mortgage backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	2,421	2,903
Gross unrealized gain	181	170
Gross unrealized losses	(5)	(10)
Estimated fair value	2,597	3,063
Asset-backed
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	301	8,084
Gross unrealized gain	11	9
Gross unrealized losses	(17)	(175)
Estimated fair value	295	7,918
Corporate non US
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	914	1,021
Gross unrealized gain	137	115
Gross unrealized losses	(1)	(1)
Estimated fair value	1,050	1,135
Government - non-U.S.
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	1,287	1,646
Gross unrealized gain	182	152
Gross unrealized losses	(1)	(2)
Estimated fair value	1,468	1,796
U.S. Government and federal agency
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	5,029	1,957
Gross unrealized gain	86	56
Gross unrealized losses	0	0
Estimated fair value	5,115	2,013
Retained Interest [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	16	16
Gross unrealized gain	1	1
Gross unrealized losses	0	0
Estimated fair value	17	17
Available-for-sale Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	144	197
Gross unrealized gain	55	58
Gross unrealized losses	(1)	(1)
Estimated fair value	198	254
Trading Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized cost	19	21
Gross unrealized gain	0	0
Gross unrealized losses	0	0
Estimated fair value	19	21
Mortgage-backed Securities, Issued by Private Enterprises [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments	34
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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-Name Accounting Standards Codification

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