Derivative Instruments - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Derivative [Line Items]
Derivatives designated as cash flow hedges gain (loss), amount expected to be reclassified to future net income (loss), net of tax	$ 2,070	[1]	$ 1,319	[1]	$ 1,909	[1]	$ 2,009	[1]
Year by which all forecasted transactions associated with qualifying cash flow hedges are expected to occur	2047
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	57
Derivative assets | Subject to enforceable master netting arrangement
Derivative [Line Items]
Amount to claim from counterparties if the downgrade provisions had been triggered	47	[2]	27	[2]
Derivative liabilities | Subject to enforceable master netting arrangement
Derivative [Line Items]
Amount required for disbursement to counterparties if the downgrade provisions had been triggered	$ 2	[3]	$ 5	[3]

[1] See note 5 for additional information.

[2] Included $25 million of accruals on derivatives classified as other assets and does not include amounts related to embedded derivatives as of December 31, 2014 and 2013.

[3] Included $6 million and $7 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 December 31, 2014 and 2013, respectively.