Debt - Narrative (Detail) - USD ($)	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Debt Instrument [Line Items]
Interest expense for premium paid for early redemption of notes in excess of carrying value	$ 114,000,000	$ 115,000,000
5.72% Notes, due 2019
Debt Instrument [Line Items]
Long-term debt, interest rate	5.72%
Long-term debt			$ 500,000,000
Redemption amount	$ 518,000,000
Loss on prepayment of debt redemption	$ 19,000,000