Investment Securities (Investment Table) (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment		$ 839
Available-for-sale Securities, Amortized Cost Basis	$ 23,266	19,293
Available-for-sale Securities, Gross Unrealized Gains	112	68
Available-for-sale Securities, Gross Unrealized Losses	(279)	(435)
Available-for-sale securities	23,099	18,926
Held-to-maturity securities	1,839	839
Held-to-maturity Securities, Fair Value	1,807	789
Fair Value Hedge Assets	304
Deposit Assets	12	14
Pledged Assets Separately Reported, Securities Pledged for Federal Home Loan Bank, at Fair Value	6,705	4,881
Financial Instruments Owned and Pledged as Collateral, Amount Eligible to be Repledged by Counterparty	1,339	737
Cash Equivalents, at Carrying Value	304	$ 291
Held-to-Maturity Debt Securities, Yield		2.90%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount		$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield		0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount		$ 0
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield		0.00%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount		$ 0
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield		0.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount		$ 839
Held-to-Maturity Securities, Due After Ten Years, Yield		2.90%
Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	22,703	$ 18,651
Available-for-sale Debt Securities Gross Unrealized Gain	100	61
Available-for-sale Debt Securities, Gross Unrealized Loss	(229)	(381)
Available-for-sale Securities, Debt Securities	22,574	18,331
US Treasury and Government [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	2,112	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	2,073	1,620
US States and Political Subdivisions Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	849	794
Available-for-sale Debt Securities Gross Unrealized Gain	12	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(10)	(19)
Available-for-sale Securities, Debt Securities	851	782
Foreign Government Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	157	157
Available-for-sale Debt Securities Gross Unrealized Gain	2	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)	0
Available-for-sale Securities, Debt Securities	157	162
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	14,423	10,473
Available-for-sale Debt Securities Gross Unrealized Gain	54	29
Available-for-sale Debt Securities, Gross Unrealized Loss	(133)	(212)
Available-for-sale Securities, Debt Securities	14,344	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, Amortized Cost before Other than Temporary Impairment	1,799
Held-to-maturity securities	1,799	839
Held-to-maturity Securities, Unrecognized Holding Gain	4	0
Held-to-maturity Securities, Unrecognized Holding Loss	(36)	(50)
Held-to-maturity Securities, Fair Value	$ 1,767	789
Held-to-Maturity Debt Securities, Yield	3.10%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,799
Held-to-Maturity Securities, Due After Ten Years, Yield	3.10%
Residential Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 2,326	2,162
Available-for-sale Debt Securities Gross Unrealized Gain	16	5
Available-for-sale Debt Securities, Gross Unrealized Loss	(32)	(70)
Available-for-sale Securities, Debt Securities	2,310	2,097
Commercial Mortgage Backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	509	537
Available-for-sale Debt Securities Gross Unrealized Gain	2	2
Available-for-sale Debt Securities, Gross Unrealized Loss	(2)	(2)
Available-for-sale Securities, Debt Securities	509	537
Asset-backed Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	1,036	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	1,039	1,400
Asset-backed Securities [Member] | Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	40
Held-to-maturity securities	40	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	$ 40	0
Held-to-Maturity Debt Securities, Yield	1.70%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 39
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	1.60%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 1
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	3.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 0
Held-to-Maturity Securities, Due After Ten Years, Yield	0.00%
Corporate Debt Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Debt Securities, Amortized Cost Basis	$ 1,291	1,452
Available-for-sale Debt Securities Gross Unrealized Gain	10	7
Available-for-sale Debt Securities, Gross Unrealized Loss	(10)	(16)
Available-for-sale Securities, Debt Securities	1,291	1,443
Equity Securities [Member]
Schedule of Investments [Line Items]
Available-for-sale Equity Securities, Amortized Cost Basis	563	642
Available-for-sale Equity Securities, Gross Unrealized Gain	12	7
Available-for-sale Equity Securities, Gross Unrealized Loss	(50)	(54)
Available-for-sale Securities, Equity Securities	525	595
Held-to-maturity Securities [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Amortized Cost before Other than Temporary Impairment	1,839
Held-to-maturity securities	1,839	839
Held-to-maturity Securities, Unrecognized Holding Gain	4	0
Held-to-maturity Securities, Unrecognized Holding Loss	(36)	(50)
Held-to-maturity Securities, Fair Value	$ 1,807	789
Held-to-Maturity Debt Securities, Yield	3.10%
Held-to-maturity Securities, Debt Maturities, within One Year, Net Carrying Amount	$ 0
Held-to-Maturity Debt Securities, Due in One Year or Less, Yield	0.00%
Held-to-maturity Securities, Debt Maturities, after One Through Five Years, Net Carrying Amount	$ 39
Held-to-Maturity Debt Securities, Due After One Year Through Five Years, Yield	1.60%
Held-to-maturity Securities, Debt Maturities, after Five Through Ten Years, Net Carrying Amount	$ 1
Held-to-Maturity Debt Securities, Due After Five Years Through Ten Years, Yield	3.00%
Held-to-maturity Securities, Debt Maturities, after Ten Years, Net Carrying Amount	$ 1,799
Held-to-Maturity Securities, Due After Ten Years, Yield	3.10%
Federal Home Loan Bank Certificates and Obligations (FHLB) [Member]
Schedule of Investments [Line Items]
Held-to-maturity Securities, Fair Value	$ 115	$ 87