Declared Common Stock Dividends (Parenthetical) (Detail) - $ / shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Dividends Payable [Line Items]
Dividend declared per share	$ 2.04	$ 2.16	$ 2.04
Qualified dividend as defined by the IRS
Dividends Payable [Line Items]
Dividend declared per share	0.076573
Qualified dividend as defined by the IRS
Dividends Payable [Line Items]
Dividend declared per share	0.048357
Qualified dividend as defined by the IRS
Dividends Payable [Line Items]
Dividend declared per share	0.051202
Qualified dividend as defined by the IRS
Dividends Payable [Line Items]
Dividend declared per share	$ 0.030979