Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Other Assets Fair Value [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	$ 128	$ 156
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	127	176
Fair Value Option Aggregate Difference Assets	1	(20)
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value of liabilities for which fair value option was elected	49	64
Aggregate Unpaid Principal Balance, Other borrowed funds	50	65
Difference, Other borrowed funds	(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	473	495
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	457	478
Fair Value Option Aggregate Difference Assets	16	17
Residential Mortgage [Member] | Loans [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value Of Assets For Which Fair Value Option Was Elected	758	782
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	891	919
Fair Value Option Aggregate Difference Assets	(133)	(137)
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	467	489
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	450	472
Fair Value Option Aggregate Difference Assets	17	17
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	288	279
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	306	298
Fair Value Option Aggregate Difference Assets	(18)	(19)
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	2
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	3	2
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	286	321
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	294	329
Fair Value Option Aggregate Difference Assets	(8)	(8)
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	3	4
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	4	4
Fair Value Option Aggregate Difference Assets	(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	184	182
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	291	292
Fair Value Option Aggregate Difference Assets	(107)	(110)
Commercial 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	163	396
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	183	411
Fair Value Option Aggregate Difference Assets	(20)	(15)
Commercial 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	163	396
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected	183	411
Fair Value Option Aggregate Difference Assets	(20)	(15)
Commercial 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
Aggregate Unpaid Principal Balance Of Assets For Which Fair Value Option Was Elected
Fair Value Option Aggregate Difference Assets