Share-Based Compensation - Stock Option Activity Table (Detail) - USD ($) $ / shares in Units, shares in Thousands, $ in Millions		12 Months Ended
		Dec. 31, 2017		Dec. 31, 2016	Dec. 31, 2015
Share-Based Compensation Arrangement by Share-Based Payment Award, Options, Outstanding [Roll Forward]
Shares outstanding at January 1, 2016		6,620
Shares granted		1,480
Shares exercised		0	[1]	(1,000)	(1,000)
Shares forfeited or expired		(1,530)
Shares outstanding at December 31, 2016		6,570		6,620
Shares vested or expected to vest at December 31, 2016		6,570
Shares exercisable at December 31, 2016		4,410
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Weighted-average exercise price, outstanding at January 1, 2016		$ 76.10
Granted weighted-average exercise price		49.82
Exercised weighted-average exercise price	[1]	47.20
Forfeited or expired weighted-average exercise price		70.71
Weighted-average exercise price, outstanding at December 31, 2016		71.44		$ 76.10
Weighted-average exercise price, vested or expected to vest at December 31, 2016		71.44
Weighted-average exercise price, exercisable at December 31, 2016		$ 79.86
Weighted-average remaining contractual term, outstanding at December 31, 2016		3 years 7 months 19 days
Weighted-average remaining contractual term, vested or expected to vest at December 31, 2016		3 years 7 months 19 days
Weighted-average remaining contractual term, exercisable at December 31, 2016		2 years 3 months 15 days
Aggregate intrinsic value, outstanding at December 31, 2016		$ 7.4
Aggregate intrinsic value, vested or expected to vest at December 31, 2016		7.4
Aggregate intrinsic value, exercisable at December 31, 2016		0.1
Total intrinsic value of stock options exercised during the period		$ 0.0		$ 7.0	$ 23.0

[1] The total intrinsic value of stock options exercised was zero during 2017, $7 million during 2016, and $23 million during 2015, based on the difference between the market price at the exercise date and the exercise price.