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, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	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, 2020	Dec. 31, 2019	Dec. 31, 2018
Class of Stock [Line Items]
Shares repurchased (in shares)															0	0	25,200,000
Common stock repurchased, share repurchase program																	$ 1,380
Average cost per share (in dollars per share)																	$ 54.85
Additional amount of common stock that may be repurchased			$ 650												$ 650
Cash dividends on common stock (in dollars per share)			$ 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 (in shares)		575,000
Series A, cumulative mandatory convertible preferred stock - dividend rate		8.00%
Preferred stock, par value (in dollars per share)		$ 1
Preferred stock, liquidation preference per share (in dollars per share)		$ 1,000
Series A Mandatory Convertible Preferred Stock
Class of Stock [Line Items]
Net number of common shares issued upon conversion of preferred stocks (in shares)	11,600,000