Shareholders' Equity - Common Dividends Declared Per Share (Detail) - Common Stock - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Dividends Per Share
Dividends declared, common stock (usd per share)	$ 1.6	$ 1.7
December 15, 2016
Dividends Per Share
Date declared	Dec. 15, 2016
Dividends declared, common stock (usd per share)	$ 0.40
Date of payment	Jan. 26, 2017
September 14, 2016
Dividends Per Share
Date declared	Sep. 14, 2016
Dividends declared, common stock (usd per share)	$ 0.40
Date of payment	Oct. 26, 2016
June 15, 2016
Dividends Per Share
Date declared	Jun. 15, 2016
Dividends declared, common stock (usd per share)	$ 0.40
Date of payment	Jul. 26, 2016
March 15, 2016
Dividends Per Share
Date declared	Mar. 15, 2016
Dividends declared, common stock (usd per share)	$ 0.40
Date of payment	Apr. 26, 2016
December 15, 2015
Dividends Per Share
Date declared		Dec. 15, 2015
Dividends declared, common stock (usd per share)		$ 0.40
Date of payment		Jan. 26, 2016
September 15, 2015
Dividends Per Share
Date declared		Sep. 15, 2015
Dividends declared, common stock (usd per share)		$ 0.40
Date of payment		Oct. 27, 2015
June 15, 2015
Dividends Per Share
Date declared		Jun. 15, 2015
Dividends declared, common stock (usd per share)		$ 0.45
Date of payment		Jul. 28, 2015
March 17, 2015
Dividends Per Share
Date declared		Mar. 17, 2015
Dividends declared, common stock (usd per share)		$ 0.45
Date of payment		Apr. 28, 2015