Loans - Status of Consumer Loan Portfolio (Detail) - USD ($) $ in Millions		Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017
Financing Receivable, Recorded Investment [Line Items]
Accruing Loans Contractually Past Due 90 days or More		$ 20	$ 18
Total loans		66,756	72,563	$ 67,593
Consumer Loans [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans		19,086	19,030
Nonaccrual Loans		468	481
Accruing Loans Contractually Past Due 90 days or More		19	17
Total loans		19,573	19,528
Consumer Loans [Member] | Residential Mortgage [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans		16,970	16,859
Nonaccrual Loans	[1],[2],[3]	406	414
Accruing Loans Contractually Past Due 90 days or More		0	0
Total loans		17,376	17,273	17,196
Consumer Loans [Member] | Home Equity Mortgages [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans		965	1,124
Nonaccrual Loans	[1],[3]	62	67
Accruing Loans Contractually Past Due 90 days or More		0	0
Total loans		1,027	1,191	1,234
Consumer Loans [Member] | Credit Cards [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans		894	712
Nonaccrual Loans		0	0
Accruing Loans Contractually Past Due 90 days or More		13	9
Total loans		907	721	656
Consumer Loans [Member] | Other consumer [Member]
Financing Receivable, Recorded Investment [Line Items]
Performing Loans		257	335
Nonaccrual Loans		0	0
Accruing Loans Contractually Past Due 90 days or More		6	8
Total loans		$ 263	$ 343	$ 379

[1] At September 30, 2018 and December 31, 2017, nonaccrual consumer mortgage loans held for investment include $334 million and $360 million, respectively, of loans that are carried at the lower of amortized cost or fair value of the collateral less cost to sell.

[2] Nonaccrual consumer mortgage loans for all periods does not include guaranteed loans purchased from the Government National Mortgage Association. Repayment of these loans is predominantly insured by the Federal Housing Administration and as such, these loans have different risk characteristics from the rest of our consumer loan portfolio.

[3] Nonaccrual consumer mortgage loans held for investment include all loans which are 90 or more days contractually delinquent as well as loans discharged under Chapter 7 bankruptcy and not re-affirmed and second lien loans where the first lien loan that we own or service is 90 or more days contractually delinquent.