Fair Value Measurements - Assets and Liabilities Recorded as Fair Value on Nonrecurring Basis (Detail) - USD ($) $ in Millions		3 Months Ended		9 Months Ended
		Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016	Dec. 31, 2016
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)		$ 42	$ (25)	$ 94	$ (406)
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		0		0		$ 0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		65		65		148
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		336		336		1,047
Residential mortgages [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[1]	0	(17)	7	(61)
Residential mortgages [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	0		0		0
Residential mortgages [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	0		0		6
Residential mortgages [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	3		3		769
Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[2]	(2)	(10)	(10)	(19)
Consumer loans [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[2]	0		0		0
Consumer loans [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[2]	21		21		46
Consumer loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[2]	0		0		0
Commercial Loans Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[3]	4	(7)	4	(37)
Commercial Loans Held for Sale [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[3]	0		0		0
Commercial Loans Held for Sale [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[3]	34		34		79
Commercial Loans Held for Sale [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[3]	0		0		0
Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[4]	38	7	87	(295)
Impaired commercial loans [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[4]	0		0		0
Impaired commercial loans [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[4]	0		0		0
Impaired commercial loans [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[4]	333		333		278
Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Total Gains (Losses)	[5]	2	$ 2	6	$ 6
Real Estate Owned [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[5]	0		0		0
Real Estate Owned [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[5]	10		10		17
Real Estate Owned [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[5]	0		0		0
Estimate of fair value [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring		401		401		1,195
Estimate of fair value [Member] | Residential mortgages [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[1]	3		3		775
Estimate of fair value [Member] | Consumer loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[2]	21		21		46
Estimate of fair value [Member] | Commercial Loans Held for Sale [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[3]	34		34		79
Estimate of fair value [Member] | Impaired commercial loans [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[4]	333		333		278
Estimate of fair value [Member] | Real Estate Owned [Member]
Fair Value, Assets and Liabilities Measured on a Nonrecurring Basis [Line Items]
Assets, Fair Value Disclosure, Nonrecurring	[5]	$ 10		$ 10		$ 17

[1] At September 30, 2017 and December 31, 2016, the fair value of the loans held for sale was below cost. Certain residential mortgage loans held for sale have been classified as Level 3 fair value measurements within the fair value hierarchy, including certain residential mortgage loans held for sale for which the underlying real estate properties used to determine fair value are illiquid assets as a result of market conditions and, at December 31, 2016, certain residential mortgage loans which were transferred to held for sale during 2016 and substantially sold during the nine months ended September 30, 2017 for which significant inputs in estimating fair value were unobservable. Additionally, the fair value of these properties is affected by, among other things, the location, the payment history and the completeness of the loan documentation.

[2] Represents residential mortgage loans held for investment whose carrying amount was reduced during the periods presented based on the fair value of the underlying collateral. Total gains (losses) for the three and nine months ended September 30, 2016 include amounts recorded on loans that were subsequently transferred to held for sale.

[3] At September 30, 2017 and December 31, 2016, the fair value of the loans held for sale was below cost.

[4] Certain commercial loans have undergone troubled debt restructurings and are considered impaired. As a matter of practical expedient, we measure the credit impairment of a collateral-dependent loan based on the fair value of the collateral asset. The collateral often involves real estate properties that are illiquid due to market conditions. As a result, these loans are classified as a Level 3 fair value measurement within the fair value hierarchy.

[5] Real estate owned is required to be reported on the balance sheet net of transactions costs. The real estate owned amounts in the table above reflect the fair value unadjusted for transaction costs.