Credit Quality - Recorded Investment in Impaired Loans and Related Allowance by Class (Parenthetical) (Details) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 1,547	$ 1,382
Commercial Portfolio Segment | TDR on accrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	32	60
Commercial Portfolio Segment | TDR on nonaccrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	204	147
Residential Mortgage Loans | TDR on accrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	740	724
Residential Mortgage Loans | TDR on nonaccrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	12	12
Consumer Portfolio Segment | TDR on accrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	218	237
Consumer Portfolio Segment | TDR on nonaccrual status
Financing Receivable, Impaired [Line Items]
Unpaid Principal Balance	$ 44	$ 41