Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Schedule of Investments [Line Items]
Held-to-maturity securities	$ 1,967		$ 1,899
Held-to-maturity Securities, Fair Value	1,895		1,865
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	839		1,000
US Treasury and Government [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,855		1,831
Available-for-sale Debt Securities Gross Unrealized Gain	0	$ 0
Available-for-sale Debt Securities, Gross Unrealized Loss	(86)	(54)
Available-for-sale Securities, Debt Securities	1,769		1,777
US States and Political Subdivisions Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	845		850
Available-for-sale Debt Securities Gross Unrealized Gain	5	11
Available-for-sale Debt Securities, Gross Unrealized Loss	(19)	(7)
Available-for-sale Securities, Debt Securities	831		854
Foreign Government Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	150		153
Available-for-sale Debt Securities Gross Unrealized Gain	1	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)	(1)
Available-for-sale Securities, Debt Securities	149		154
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	15,316		14,412
Available-for-sale Debt Securities Gross Unrealized Gain	4	35
Available-for-sale Debt Securities, Gross Unrealized Loss	(437)	(156)
Available-for-sale Securities, Debt Securities	14,883		14,291
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member] \| Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,936		1,863
Held-to-maturity Securities, Unrecognized Holding Gain	0	3
Held-to-maturity Securities, Unrecognized Holding Loss	(72)	(37)
Held-to-maturity Securities, Fair Value	1,864		1,829
Residential Mortgage Backed Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,456		2,517
Available-for-sale Debt Securities Gross Unrealized Gain	3	11
Available-for-sale Debt Securities, Gross Unrealized Loss	(75)	(34)
Available-for-sale Securities, Debt Securities	2,384		2,494
Commercial Mortgage Backed Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	582		541
Available-for-sale Debt Securities Gross Unrealized Gain	1	1
Available-for-sale Debt Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale Securities, Debt Securities	580		541
Asset-backed Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	901		933
Available-for-sale Debt Securities Gross Unrealized Gain	2	4
Available-for-sale Debt Securities, Gross Unrealized Loss	(3)	(1)
Available-for-sale Securities, Debt Securities	900		936
Asset-backed Securities [Member] \| Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	31		36
Held-to-maturity Securities, Unrecognized Holding Gain	0	0
Held-to-maturity Securities, Unrecognized Holding Loss	0	0
Held-to-maturity Securities, Fair Value	31		36
Corporate Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,263		1,262
Available-for-sale Debt Securities Gross Unrealized Gain	1	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(34)	(11)
Available-for-sale Securities, Debt Securities	1,230		1,256
Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	23,368		22,499
Available-for-sale Debt Securities Gross Unrealized Gain	17	69
Available-for-sale Debt Securities, Gross Unrealized Loss	(659)	(265)
Available-for-sale Securities, Debt Securities	22,726		22,303
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	1,967		1,899
Held-to-maturity Securities, Unrecognized Holding Gain	0	3
Held-to-maturity Securities, Unrecognized Holding Loss	(72)	$ (37)
Held-to-maturity Securities, Fair Value	1,895		1,865
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	8,000		7,800
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member] \| Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	993		664
Insurance Operations [Member]
Schedule of Investments [Line Items]
Deposit Assets	$ 12		$ 12

This item represents the cost of debt securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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