Stockholders' Equity - Company's Restricted Stock Grants and Stock Options (Detail)	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Number of Shares [Roll Forward]
Options granted | shares	271,700,000
Options unvested, ending balance | shares	271,700,000
Share-based Compensation Arrangement by Share-based Payment Award, Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, Options granted | $ / shares	$ 30.65
Weighted-average grant date fair value, Options unvested, ending balance | $ / shares	$ 30.65
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Shares unvested, beginning balance | shares	823,600,000
Shares granted | shares	402,000,000.0
Shares for which restrictions lapsed | shares	(225,300,000)
Shares unvested, ending balance | shares	1,000,300,000
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Weighted-average grant date fair value, beginning balance | $ / shares	$ 36.69
Weighted-average grant date fair value, shares granted | $ / shares	31.12
Weighted-average grant date fair value, shares for which restrictions lapsed | $ / shares	30.50
Weighted-average grant date fair value, ending balance | $ / shares	$ 35.59