Credit Quality (Recorded Investment in Impaired Loans and Related Allowance by Class) (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Impaired
Unpaid Principal Balance	$ 1,426	$ 1,382
Commercial Portfolio Segment | TDR on accrual status
Financing Receivable, Impaired
Unpaid Principal Balance	59	60
Commercial Portfolio Segment | TDR on nonaccrual status
Financing Receivable, Impaired
Unpaid Principal Balance	159	147
Residential Mortgage Loans | TDR on accrual status
Financing Receivable, Impaired
Unpaid Principal Balance	724	724
Residential Mortgage Loans | TDR on nonaccrual status
Financing Receivable, Impaired
Unpaid Principal Balance	10	12
Consumer Portfolio Segment | TDR on accrual status
Financing Receivable, Impaired
Unpaid Principal Balance	226	237
Consumer Portfolio Segment | TDR on nonaccrual status
Financing Receivable, Impaired
Unpaid Principal Balance	$ 46	$ 41