Amount of cash and cash equivalents restricted as to withdrawal or usage. Cash includes, but is not limited to, currency on hand, demand deposits with banks or financial institutions, and other accounts with general characteristics of demand deposits. Cash equivalents include, but are not limited to, short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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

Supplemental Cash Flow Information - Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents (Detail) - USD ($) $ in Millions	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents	$ 1,531	$ 1,429	$ 2,432	$ 4,674
Cash and cash equivalents [Member]
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents	1,394	1,295
Restricted cash and restricted cash equivalents	118	139
Restricted cash and restricted cash equivalents included in Other Assets [Member]
Cash and Cash Equivalents [Line Items]
Cash, Cash Equivalents, Restricted Cash, and Restricted Cash Equivalents	$ 137	$ 134