Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 18,146	$ 17,350
Available-for-sale Securities, Gross Unrealized Gains	211	96
Available-for-sale Securities, Gross Unrealized Losses	(177)	(289)
Available-for-sale securities	18,180	17,157
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	118	0
Total agency backed bonds	9,585	7,544
Deposit Assets	15	14
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	764	745
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	764	2,506
Cash Equivalents, at Carrying Value	1,400	1,000
Held-to-maturity Securities, Fair Value	118	0
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Unrealized Gain on Securities	0	0
Unrealized Gain (Loss) on Investments	0	0
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	17,356	16,542
Available-for-sale Debt Securities Gross Unrealized Gain	199	93
Available-for-sale Debt Securities, Gross Unrealized Loss	(91)	(195)
Available-for-sale Securities, Debt Securities	17,464	16,440
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	345	1,760
Available-for-sale Debt Securities Gross Unrealized Gain	11	0
Available-for-sale Debt Securities, Gross Unrealized Loss	0	(19)
Available-for-sale Securities, Debt Securities	356	1,741
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	721	693
Available-for-sale Debt Securities Gross Unrealized Gain	23	24
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(1)
Available-for-sale Securities, Debt Securities	743	716
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	181	169
Available-for-sale Debt Securities Gross Unrealized Gain	10	8
Available-for-sale Debt Securities, Gross Unrealized Loss	0	0
Available-for-sale Securities, Debt Securities	191	177
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	12,241	10,459
Available-for-sale Debt Securities Gross Unrealized Gain	129	52
Available-for-sale Debt Securities, Gross Unrealized Loss	(57)	(145)
Available-for-sale Securities, Debt Securities	12,313	10,366
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	515	486
Available-for-sale Debt Securities Gross Unrealized Gain	0	0
Available-for-sale Debt Securities, Gross Unrealized Loss	(15)	(5)
Available-for-sale Securities, Debt Securities	500	481
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,792	1,762
Available-for-sale Debt Securities Gross Unrealized Gain	0	1
Available-for-sale Debt Securities, Gross Unrealized Loss	(11)	(8)
Available-for-sale Securities, Debt Securities	1,781	1,755
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,561	1,213
Available-for-sale Debt Securities Gross Unrealized Gain	26	8
Available-for-sale Debt Securities, Gross Unrealized Loss	(7)	(17)
Available-for-sale Securities, Debt Securities	1,580	1,204
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	790	808
Available-for-sale Equity Securities, Gross Unrealized Gain	12	3
Available-for-sale Equity Securities, Gross Unrealized Loss	(86)	(94)
Available-for-sale Securities, Equity Securities	$ 716	$ 717

Total agency backed bonds, available for sale.

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