Investments - Debt Securities At Fair Value (Detail) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Debt securities, at fair value	$ 16,570	$ 12,117
Corporate debt securities [Member]
Debt securities, at fair value	11,821	8,434
Securities backed by real estate [Member]
Debt securities, at fair value	2,619	1,775
Other [Member]
Debt securities, at fair value	$ 2,130	$ 1,908

Amount of investment in debt security measured at fair value with change in fair value recognized in net income (trading).

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Name:	us-gaap_TradingSecuritiesDebt
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant