Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Mar. 31, 2018	Dec. 31, 2017
Other Assets Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	$ 216	$ 216
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	221	212
Fair Value Option Aggregate Difference Assets	(5)	4
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of liabilities for which fair value option was elected	56	84
Aggregate Unpaid Principal Balance, Other borrowed funds	57	85
Difference, Other borrowed funds	(1)	(1)
Commercial Real Estate [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	245	830
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	266	845
Fair Value Option Aggregate Difference Assets	(21)	(15)
Commercial Real Estate [Member] | Performing Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	244	828
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	264	842
Fair Value Option Aggregate Difference Assets	(20)	(14)
Commercial Real Estate [Member] | Nonaccrual Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	1	2
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	2	3
Fair Value Option Aggregate Difference Assets	(1)	(1)
Residential Mortgage [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	617	832
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	605	807
Fair Value Option Aggregate Difference Assets	12	25
Residential Mortgage [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	813	869
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	970	1,028
Fair Value Option Aggregate Difference Assets	(157)	(159)
Residential Mortgage [Member] | Loans 90 Days Or More Past Due [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	3	3
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	3	3
Residential Mortgage [Member] | Loans 90 Days Or More Past Due [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	334	421
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	344	431
Fair Value Option Aggregate Difference Assets	(10)	(10)
Residential Mortgage [Member] | Performing Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	604	822
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	591	796
Fair Value Option Aggregate Difference Assets	13	26
Residential Mortgage [Member] | Performing Loans [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	290	251
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	319	280
Fair Value Option Aggregate Difference Assets	(29)	(29)
Residential Mortgage [Member] | Nonaccrual Loans [Member] | Loans Held For Sale [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	10	7
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	11	8
Fair Value Option Aggregate Difference Assets	(1)	(1)
Residential Mortgage [Member] | Nonaccrual Loans [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	189	197
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	307	317
Fair Value Option Aggregate Difference Assets	$ (118)	$ (120)