Derivative Instruments - Additional Information (Detail) - USD ($) $ in Millions		9 Months Ended
		Sep. 30, 2017	Jun. 30, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Derivatives designated as cash flow hedges gain (loss), amount expected to be reclassified to future net income (loss), net of tax		$ 2,052	$ 2,064	$ 2,085	$ 2,493	$ 2,439	$ 2,045
Year by which all forecasted transactions associated with qualifying cash flow hedges are expected to occur		2057
Derivatives designated as cash flow hedges gain (loss), amount expected to be reclassified to net income (loss) in the next 12 months, net of tax		$ 95
Amount reclassified to net income in connection with forecasted transactions that were no longer considered probable of occurring		2
Derivative assets | Subject to enforceable master netting arrangement
Derivative [Line Items]
Amount to claim from counterparties if the downgrade provisions had been triggered	[1]	82		86
Derivative liabilities | Subject to enforceable master netting arrangement
Derivative [Line Items]
Amounts required for disbursement to counterparties if the downgrade provisions had been triggered	[2]	$ 0		$ 2

[1] Included $1 million and $16 million of accruals on derivatives classified as other assets and does not include amounts related to embedded derivatives as of September 30, 2017 and December 31, 2016, respectively.

[2] Included $2 million and $5 million of accruals on derivatives classified as other liabilities and does not include amounts related to embedded derivatives and derivatives related to securitization entities as of September 30, 2017 and December 31, 2016, respectively.