Summary of Status of Senior Executive Plans (Detail) - $ / shares shares in Millions		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Shares
Granted		1.2	1.5	2.3
Vested		(0.8)	(0.6)	(1.2)
Restricted Stock | Executive Officer
Shares
Balance, at beginning of year		0.7
Granted		1.1	1.4	1.6
Vested	[1]	(0.7)	(0.5)	(0.6)
Forfeited/expired		(0.2)	(0.2)	(1.0)
Balance, at end of year		0.9	0.7
Issued in calendar year	[1]	0.3	0.3	0.2
Fair Value
Balance, at beginning of year		$ 14
Granted		16	$ 15	$ 18
Vested	[1]	17	20	19
Forfeited/expired		17	20	19
Balance, at end of year		14	14
Issued in calendar year	[1]	$ 20	$ 19	$ 15

[1] Shares that vest at December 31 of each year are issued to the employees in the first quarter of the following year, although the requisite service period is complete. Accordingly, the 0.3 million shares issued in 2018 include shares vested at December 31, 2017, after adjusting for shares withheld to meet employee tax requirements. The shares withheld for employee tax requirements were valued at $4.8 million, $4.9 million and $2.4 million for 2018, 2017 and 2016, respectively.