Capital Stock - Common Stock (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Feb. 28, 2018
Class of Stock [Line Items]
Stock repurchase program, authorized amount				$ 100,000,000
Stock repurchased during period (in shares)	883,000	0
Stock repurchased during period, average price (in dollars per share)	$ 16.81
Stock repurchased during period	$ 14,834,000	$ 0	$ 0
Common dividends declared	$ 375,017,000	$ 376,579,000	$ 458,735,000
Dividends declared per share of common stock (usd per share)	$ 2	$ 2.00
Regular Dividend
Class of Stock [Line Items]
Common dividends declared	$ 375,000,000	$ 377,000,000