Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Available-for-sale Securities, Amortized Cost Basis	$ 23,052	$ 19,293
Available-for-sale Securities, Gross Unrealized Gains	82	68
Available-for-sale Securities, Gross Unrealized Losses	(313)	(435)
Available-for-sale securities	22,821	18,926
Held-to-maturity securities	1,899	839
Held-to-maturity Securities, Fair Value	1,865	789
Deposit Assets	12	14
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,025	737
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	22,499	18,651
Available-for-sale Debt Securities Gross Unrealized Gain	69	61
Available-for-sale Debt Securities, Gross Unrealized Loss	(265)	(381)
Available-for-sale Securities, Debt Securities	22,303	18,331
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,831	1,680
Available-for-sale Debt Securities Gross Unrealized Gain	0	0
Available-for-sale Debt Securities, Gross Unrealized Loss	(54)	(60)
Available-for-sale Securities, Debt Securities	1,777	1,620
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	850	794
Available-for-sale Debt Securities Gross Unrealized Gain	11	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(7)	(19)
Available-for-sale Securities, Debt Securities	854	782
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	153	157
Available-for-sale Debt Securities Gross Unrealized Gain	2	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	0
Available-for-sale Securities, Debt Securities	154	162
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	14,412	10,473
Available-for-sale Debt Securities Gross Unrealized Gain	35	29
Available-for-sale Debt Securities, Gross Unrealized Loss	(156)	(212)
Available-for-sale Securities, Debt Securities	14,291	10,290
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,863	839
Held-to-maturity Securities, Unrecognized Holding Gain	3	0
Held-to-maturity Securities, Unrecognized Holding Loss	(37)	(50)
Held-to-maturity Securities, Fair Value	1,829	789
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,517	2,162
Available-for-sale Debt Securities Gross Unrealized Gain	11	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(34)	(70)
Available-for-sale Securities, Debt Securities	2,494	2,097
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	541	537
Available-for-sale Debt Securities Gross Unrealized Gain	1	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(2)
Available-for-sale Securities, Debt Securities	541	537
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	933	1,396
Available-for-sale Debt Securities Gross Unrealized Gain	4	6
Available-for-sale Debt Securities, Gross Unrealized Loss	(1)	(2)
Available-for-sale Securities, Debt Securities	936	1,400
Asset-backed Securities [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	36	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	36	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	5	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(11)	(16)
Available-for-sale Securities, Debt Securities	1,256	1,443
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	553	642
Available-for-sale Equity Securities, Gross Unrealized Gain	13	7
Available-for-sale Equity Securities, Gross Unrealized Loss	(48)	(54)
Available-for-sale Securities, Equity Securities	518	595
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,899	839
Held-to-maturity Securities, Unrecognized Holding Gain	3	0
Held-to-maturity Securities, Unrecognized Holding Loss	(37)	(50)
Held-to-maturity Securities, Fair Value	1,865	789
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Fair Value	664	87
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	$ 7,804	$ 4,881