Fair Values of Assets and Liabilities - Balances of Assets and Liabilities Measured at Fair Value on Recurring Basis (Parenthetical) (Detail) - USD ($) $ in Millions	Mar. 31, 2019	Dec. 31, 2018
Fair Value Disclosures [Abstract]
Equity investments without readily determinable fair values	$ 86	$ 86

Amount of investment in equity security without readily determinable fair value.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 321
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=84241550&loc=SL75117539-209714

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