Supplemental Financial Information - Supplemental Financial Position (Additional Information) (Detail) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Balance Sheet Statements, Captions [Line Items]
Principal amount	$ 125.6	$ 243.6
3.875% senior notes due 2023
Condensed Balance Sheet Statements, Captions [Line Items]
Interest rate on senior notes (as a percent)	3.875%	3.875%	3.875%
5.625% senior notes due 2043
Condensed Balance Sheet Statements, Captions [Line Items]
Interest rate on senior notes (as a percent)	5.625%	5.625%	5.625%