Long-Term Incentive Employee Compensation Rollforward of Outstanding Stock Options (Detail) - $ / shares shares in Millions	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Shares
Beginning Balance, Shares	1.4	1.7	1.9
Stock Options Granted, Shares		0.4	0.2
Stock Options Exercised, Shares	(0.5)	(0.6)	(0.3)
Stock Options Canceled or Expired, Shares		(0.1)	(0.1)
Stock Options Outstanding at the end of Year, Shares	0.9	1.4	1.7
Stock Options Exercisable at the end of year, Shares	0.5	0.8	1.1
Weighted Average Exercise Price
Beginning Balance, Weighted Average Exercise Price	$ 30.57	$ 27.10	$ 24.20
Stock Options Granted, Weighted Average Exercise Price	0	33.01	41.52
Stock Options Exercised, Weighted Average Exercise Price	22.95	20.88	19.87
Stock Options Canceled or Expired, Weighted Average Exercise Price	0	39.03	35.95
Outstanding, Weighted Average Exercise Price	34.07	30.57	27.10
Stock Options Exercisable at the end of year, Weighted Average Exercise Price	$ 32.24	$ 24.41	$ 21.75