Outstanding and Weighted Average Common Shares - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions		1 Months Ended	3 Months Ended												12 Months Ended
	Jan. 31, 2019	Feb. 29, 2016	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Class Of Stock [Line Items]
Series A, cumulative mandatory convertible preferred stock - dividend rate															8.00%	8.00%
Preferred stock, par value			$ 1.00				$ 1.00								$ 1.00	$ 1.00
Preferred stock, liquidation preference per share			$ 1,000				1,000								$ 1,000	$ 1,000
Net proceeds from issuance of common stock and Mandatory convertible preferred stock, after deducting underwriting discounts, commissions, and offering expenses		$ 1,600																$ 1,600
Common stock repurchased, share repurchase program																$ 1,380	$ 120
Common stock repurchased, share repurchase program, share															0	25,200,000	2,600,000
Additional amount of common stock that may be repurchased			$ 650												$ 650
Average cost per share																$ 54.85	$ 45.67
Cash dividends on common stock			$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 0.25	$ 1.00	$ 1.00	$ 1.00
Series A Mandatory Convertible Preferred Stock
Class Of Stock [Line Items]
Shares of stock issued		575,000
Series A, cumulative mandatory convertible preferred stock - dividend rate		8.00%
Preferred stock, par value		$ 1
Preferred stock, liquidation preference per share		$ 1,000
Series A Mandatory Convertible Preferred Stock | Final Average Price, Exceeds $45.83
Class Of Stock [Line Items]
Shares covered by cap call		12,550,000
Series A Mandatory Convertible Preferred Stock | Minimum
Class Of Stock [Line Items]
Number of shares issued for each share of preferred stock that is converted		21.822
Series A Mandatory Convertible Preferred Stock | Maximum
Class Of Stock [Line Items]
Number of shares issued for each share of preferred stock that is converted		25.642
Series A Mandatory Convertible Preferred Stock
Class Of Stock [Line Items]
Number of shares issued for each share of preferred stock that is converted			21.822												21.822
Common stock issuance following preferred stock conversion	12,500,000														12,500,000
Number of common shares received from capped call upon conversion of preferred stocks	900,000														900,000
Net number of common shares issued upon conversion of preferred stocks	11,600,000														11,600,000
Common Stock
Class Of Stock [Line Items]
Shares of stock issued		28,750,000
Common stock repurchased, share repurchase program																$ 25	$ 3