Capital Stock - Common Stock (Detail) - USD ($) $ / shares in Units, shares in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Class of Stock [Line Items]
Stock repurchase program, authorized amount	$ 150,000,000		$ 150,000,000
Stock repurchased during period (in shares)			1.4
Stock repurchased during period, average price (in dollars per share)			$ 15.34
Stock repurchased during period			$ 22,066,000	$ 0
Remaining authorized repurchase amount	128,000,000		128,000,000
Common dividends declared	$ 70,050,000	$ 94,590,000	$ 163,530,000	$ 188,204,000
Dividends declared per share of common stock (usd per share)	$ 0.30	$ 0.50	$ 0.80	$ 1.00
Regular Dividend
Class of Stock [Line Items]
Common dividends declared	$ 70,000,000	$ 95,000,000	$ 164,000,000	$ 188,000,000