Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 21,997	$ 19,293
Available-for-sale Securities, Gross Unrealized Gains	90	68
Available-for-sale Securities, Gross Unrealized Losses	(323)	(435)
Available-for-sale securities	21,764	18,926
Held-to-maturity securities	1,189	839
Held-to-maturity Securities, Unrecognized Holding Gain	2	0
Held-to-maturity Securities, Unrecognized Holding Loss	(35)	(50)
Held-to-maturity Securities, Fair Value	1,156	789
Deposit Assets	12	14
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	3,316	4,881
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,420	737
Cash Equivalents, at Carrying Value	1,200	291
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	21,448	18,651
Available-for-sale Debt Securities Gross Unrealized Gain	81	61
Available-for-sale Debt Securities, Gross Unrealized Loss	(270)	(381)
Available-for-sale Securities, Debt Securities	21,259	18,331
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,891	1,680
Available-for-sale Debt Securities Gross Unrealized Gain	0	0
Available-for-sale Debt Securities, Gross Unrealized Loss	(39)	(60)
Available-for-sale Securities, Debt Securities	1,852	1,620
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	780	794
Available-for-sale Debt Securities Gross Unrealized Gain	13	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(11)	(19)
Available-for-sale Securities, Debt Securities	782	782
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	148	157
Available-for-sale Debt Securities Gross Unrealized Gain	2	5
Available-for-sale Debt Securities, Gross Unrealized Loss	0	0
Available-for-sale Securities, Debt Securities	150	162
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	13,809	10,473
Available-for-sale Debt Securities Gross Unrealized Gain	39	29
Available-for-sale Debt Securities, Gross Unrealized Loss	(172)	(212)
Available-for-sale Securities, Debt Securities	13,676	10,290
Held-to-maturity securities	1,143	839
Held-to-maturity Securities, Unrecognized Holding Gain	2	0
Held-to-maturity Securities, Unrecognized Holding Loss	(35)	(50)
Held-to-maturity Securities, Fair Value	1,110	789
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,063	2,162
Available-for-sale Debt Securities Gross Unrealized Gain	11	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(36)	(70)
Available-for-sale Securities, Debt Securities	2,038	2,097
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	474	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	475	537
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,010	1,396
Available-for-sale Debt Securities Gross Unrealized Gain	6	6
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)	(2)
Available-for-sale Securities, Debt Securities	1,014	1,400
Held-to-maturity securities	46	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	46	0
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,273	1,452
Available-for-sale Debt Securities Gross Unrealized Gain	8	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(9)	(16)
Available-for-sale Securities, Debt Securities	1,272	1,443
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	549	642
Available-for-sale Equity Securities, Gross Unrealized Gain	9	7
Available-for-sale Equity Securities, Gross Unrealized Loss	(53)	(54)
Available-for-sale Securities, Equity Securities	505	595
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Fair Value	$ 0	$ 87