Accumulated Other Comprehensive Income (Loss) and Other Comprehensive Income (Loss) - Schedule of Components of Other Comprehensive Income (Loss) that have been Reclassified (Detail) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Other comprehensive income (loss), before income taxes	$ (619.0)	$ (680.7)
Total tax expense (benefit) for the period	(22.8)	3.0
Other comprehensive income (loss), net of tax	(30.3)	(2.4)
Other Comprehensive Loss Reclassifications [Member] | Change in Derivative Cash Flow Hedges [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Other comprehensive income (loss), before income taxes	(0.4)	(7.4)
Total tax expense (benefit) for the period	(0.2)	(2.8)
Other comprehensive income (loss), net of tax	(0.2)	(4.6)
Other Comprehensive Loss Reclassifications [Member] | Change in Pension and OPEB Liability Adjustments [Member]
Reclassification Adjustment Out of Accumulated Other Comprehensive Income [Line Items]
Other comprehensive income (loss), before income taxes	(2.4)	(1.6)
Total tax expense (benefit) for the period	(0.9)	(0.6)
Other comprehensive income (loss), net of tax	$ (1.5)	$ (1.0)