Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
Jun. 30, 2018	Dec. 31, 2017
Schedule of Investments [Line Items]
Held-to-maturity securities	$ 2,089	$ 1,899
Held-to-maturity Securities, Fair Value	2,007	1,865
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,200	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	1,963	1,831
Available-for-sale Debt Securities Gross Unrealized Gain	1	0
Available-for-sale Debt Securities, Gross Unrealized Loss	(90)	(54)
Available-for-sale Securities, Debt Securities	1,874	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	865	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	851	854
Foreign Government Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	155	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	154	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	15,559	14,412
Available-for-sale Debt Securities Gross Unrealized Gain	4	35
Available-for-sale Debt Securities, Gross Unrealized Loss	(497)	(156)
Available-for-sale Securities, Debt Securities	15,066	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	2,062	1,863
Held-to-maturity Securities, Unrecognized Holding Gain	1	3
Held-to-maturity Securities, Unrecognized Holding Loss	(83)	(37)
Held-to-maturity Securities, Fair Value	1,980	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	2,716	2,517
Available-for-sale Debt Securities Gross Unrealized Gain	2	11
Available-for-sale Debt Securities, Gross Unrealized Loss	(93)	(34)
Available-for-sale Securities, Debt Securities	2,625	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	644	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	642	541
Asset-backed Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	870	933
Available-for-sale Debt Securities Gross Unrealized Gain	2	4
Available-for-sale Debt Securities, Gross Unrealized Loss	(4)	(1)
Available-for-sale Securities, Debt Securities	868	936
Asset-backed Securities [Member] \| Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	27	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	27	36
Corporate Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,258	1,262
Available-for-sale Debt Securities Gross Unrealized Gain	1	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(43)	(11)
Available-for-sale Securities, Debt Securities	1,216	1,256
Debt Securities [Member] \| Available-for-sale Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	24,030	22,499
Available-for-sale Debt Securities Gross Unrealized Gain	17	69
Available-for-sale Debt Securities, Gross Unrealized Loss	(751)	(265)
Available-for-sale Securities, Debt Securities	23,296	22,303
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity securities	2,089	1,899
Held-to-maturity Securities, Unrecognized Holding Gain	1	3
Held-to-maturity Securities, Unrecognized Holding Loss	(83)	(37)
Held-to-maturity Securities, Fair Value	2,007	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	7,100	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	962	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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