Derivative Financial Instruments - Additional Information (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018
Derivative Instruments, Gain (Loss) [Line Items]
Decrease in valuation due to net credit risk adjustments	$ 15	$ 26
Decrease in valuation due to liquidity adjustments	15	19
Derivative liability at fair value including accrued interest and premium receivable	713	$ 752
Counterparty [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivative liability at fair value including accrued interest and premium receivable	$ 73

The aggregate fair value amounts of derivative instruments that contain credit-risk-related contingent features that are in a net liability position at the end of the reporting period. For nonderivative instruments that are designated and qualify as hedging instruments, the fair value amounts are the carrying value of the nonderivative hedging instrument, including the adjustment for the foreign currency transaction gain (loss) on that instrument.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 4H
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5624258-113959

Name:	us-gaap_DerivativeNetLiabilityPositionAggregateFairValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant