Fair Value (Fair Value Option - Fair Value and Principal Balances) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Loans Held For Sale [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	$ 842	$ 1,010
Aggregate Unpaid Principal Balance - Assets	810	998
Difference - Assets	32	12
Loans Held For Sale [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	758	1,400
Aggregate Unpaid Principal Balance - Assets	800	1,421
Difference - Assets	(42)	(21)
Loans Held For Sale [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	832	1,000
Aggregate Unpaid Principal Balance - Assets	799	988
Difference - Assets	33	12
Loans Held For Sale [Member] | Performing Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	756	1,395
Aggregate Unpaid Principal Balance - Assets	797	1,412
Difference - Assets	(41)	(17)
Loans Held For Sale [Member] | Accruing loans 90 days or more past due | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	4	4
Aggregate Unpaid Principal Balance - Assets	4	4
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	6	6
Aggregate Unpaid Principal Balance - Assets	7	6
Difference - Assets	(1)
Loans Held For Sale [Member] | Nonaccrual Loans [Member] | Commercial Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	2	5
Aggregate Unpaid Principal Balance - Assets	3	9
Difference - Assets	(1)	(4)
Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	807	893
Aggregate Unpaid Principal Balance - Assets	972	1,063
Difference - Assets	(165)	(170)
Loans [Member] | Performing Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	243	247
Aggregate Unpaid Principal Balance - Assets	273	289
Difference - Assets	(30)	(42)
Loans [Member] | Accruing loans 90 days or more past due | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	364	427
Aggregate Unpaid Principal Balance - Assets	375	428
Difference - Assets	(11)	(1)
Loans [Member] | Nonaccrual Loans [Member] | Residential Mortgage [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	200	219
Aggregate Unpaid Principal Balance - Assets	324	346
Difference - Assets	(124)	(127)
Other Assets [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Assets	230	293
Aggregate Unpaid Principal Balance - Assets	215	288
Difference - Assets	15	5
Other Borrowed Funds [Member]
Fair Value, Option, Quantitative Disclosures [Line Items]
Fair Value - Liabilities	63	81
Aggregate Unpaid Principal Balance - Liabilities	64	82
Difference - Liabilities	$ (1)	$ (1)