Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 20,651	$ 19,293
Available-for-sale Securities, Gross Unrealized Gains	71	68
Available-for-sale Securities, Gross Unrealized Losses	(414)	(435)
Available-for-sale securities	20,308	18,926
Held-to-maturity securities	1,104	839
Held-to-maturity Securities, Unrecognized Holding Gain	2	0
Held-to-maturity Securities, Unrecognized Holding Loss	(43)	50
Held-to-maturity Securities, Fair Value	1,063	789
Deposit Assets	12	14
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	3,235	4,881
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,257	737
Cash Equivalents, at Carrying Value	1,100	291
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	20,170	18,651
Available-for-sale Debt Securities Gross Unrealized Gain	62	61
Available-for-sale Debt Securities, Gross Unrealized Loss	(368)	(381)
Available-for-sale Securities, Debt Securities	19,864	18,331
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,276	1,680
Available-for-sale Debt Securities Gross Unrealized Gain	1	0
Available-for-sale Debt Securities, Gross Unrealized Loss	(52)	(60)
Available-for-sale Securities, Debt Securities	2,225	1,620
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	803	794
Available-for-sale Debt Securities Gross Unrealized Gain	9	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(17)	(19)
Available-for-sale Securities, Debt Securities	795	782
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	143	157
Available-for-sale Debt Securities Gross Unrealized Gain	3	5
Available-for-sale Debt Securities, Gross Unrealized Loss	0	0
Available-for-sale Securities, Debt Securities	146	162
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	12,054	10,473
Available-for-sale Debt Securities Gross Unrealized Gain	31	29
Available-for-sale Debt Securities, Gross Unrealized Loss	(223)	(212)
Available-for-sale Securities, Debt Securities	11,862	10,290
Held-to-maturity securities	1,052	839
Held-to-maturity Securities, Unrecognized Holding Gain	2	0
Held-to-maturity Securities, Unrecognized Holding Loss	(43)	(50)
Held-to-maturity Securities, Fair Value	1,011	789
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,053	2,162
Available-for-sale Debt Securities Gross Unrealized Gain	4	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(61)	(70)
Available-for-sale Securities, Debt Securities	1,996	2,097
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	533	537
Available-for-sale Debt Securities Gross Unrealized Gain	2	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(2)
Available-for-sale Securities, Debt Securities	534	537
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,046	1,396
Available-for-sale Debt Securities Gross Unrealized Gain	6	6
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(2)
Available-for-sale Securities, Debt Securities	1,051	1,400
Held-to-maturity securities	52	0
Held-to-maturity Securities, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	52	0
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,262	1,452
Available-for-sale Debt Securities Gross Unrealized Gain	6	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(13)	(16)
Available-for-sale Securities, Debt Securities	1,255	1,443
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	481	642
Available-for-sale Equity Securities, Gross Unrealized Gain	9	7
Available-for-sale Equity Securities, Gross Unrealized Loss	(46)	(54)
Available-for-sale Securities, Equity Securities	444	595
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Fair Value	$ 0	$ 87