Debt - Schedule of Uncommitted Bilateral Credit Facilities (Detail) - Uncommitted Bilateral Credit Facilities [Member] - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Bank Guarantee and Bilateral Letter of Credit [Member]
Debt Instrument [Line Items]
Available capacity under current credit agreement	$ 875,000,000	$ 725,000,000
Letters of credit utilized	545,000,000	572,000,000
Surety Bonds [Member]
Debt Instrument [Line Items]
Available capacity under current credit agreement	300,000,000	300,000,000
Letters of credit utilized	48,000,000	49,000,000
Bilateral Arrangements to Issue Cash Collateralized Letters Of Credit [Member]
Debt Instrument [Line Items]
Available capacity under current credit agreement	175,000,000	175,000,000
Letters of credit utilized	$ 6,000,000	$ 18,000,000