Goodwill and Mortgage Servicing Rights (Commercial and Residential Mortgage Loan Servicing Assets - Key Valuation Assumptions) (Details) $ in Millions	12 Months Ended
	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair Value	$ 1,983	$ 1,832
Mortgage Servicing Rights | Commercial Real Estate
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair Value	$ 726	$ 668	$ 576	$ 526
Weighted-average life	4 years 1 month	4 years 5 months
Decline in fair value from 10% adverse change in prepayment rate	$ 10	$ 12
Decline in fair value from 20% adverse change in prepayment rate	19	23
Decline in fair value from 10% adverse change in interest rate	19	18
Decline in fair value from 20% adverse change in interest rate	39	36
Mortgage Servicing Rights | Residential Mortgage
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Fair Value	$ 1,257	$ 1,164	$ 1,182	$ 1,063
Weighted-average life	6 years 11 months	6 years 5 months
Decline in fair value from 10% adverse change in prepayment rate	$ 41	$ 44
Decline in fair value from 20% adverse change in prepayment rate	$ 79	$ 85
Spread over the benchmark curve	8.06%	8.30%
Decline in fair value from 10% adverse change in adjusted spread	$ 37	$ 35
Decline in fair value from 20% adverse change in adjusted spread	$ 73	$ 67
Measurement Input, Constant Prepayment Rate | Mortgage Servicing Rights | Commercial Real Estate
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Servicing Asset, Measurement Input	0.0565	0.0851
Measurement Input, Constant Prepayment Rate | Mortgage Servicing Rights | Residential Mortgage
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Servicing Asset, Measurement Input	0.0869	0.1004
Measurement Input, Discount Rate | Mortgage Servicing Rights | Commercial Real Estate
Sensitivity Analysis of Fair Value of Interests Continued to be Held by Transferor, Servicing Assets or Liabilities, Impact of Adverse Change in Assumption [Line Items]
Servicing Asset, Measurement Input	0.0839	0.0781