Consolidated Statements of Comprehensive Income - USD ($) $ in Millions	3 Months Ended								9 Months Ended	12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net loss	$ (188.3)	$ (135.8)	$ (226.2)	$ (171.1)	$ (474.3)	$ (283.9)	$ (1,042.3)	$ (157.7)	$ (477.2)	$ (721.4)	$ (1,958.2)	$ (723.5)
Net change in unrealized (losses) gains on available-for-sale securities (net of respective tax benefit of ($0.0), ($0.1) and $(0.5)
Unrealized holding losses on available-for-sale securities										0.0	0.0	(3.7)
Reclassification for realized losses included in net loss										0.0	0.0	2.9
Net change in unrealized losses on available-for-sale securities										0.0	0.0	(0.8)
Net unrealized gains (losses) on cash flow hedges (net of respective tax provision (benefit) of $85.9, $72.2 and ($54.6))
Decrease in fair value of cash flow hedges										0.0	(131.3)	(195.0)
Reclassification for realized losses (gains) included in net loss										146.3	251.7	(10.2)
Net unrealized gains (losses) on cash flow hedges										146.3	120.4	(205.2)
Postretirement plans and workers' compensation obligations (net of respective tax (benefit) provision of ($1.5), $36.2 and ($10.3))
Prior service (cost) credit for the period										(4.5)	10.4	11.4
Net actuarial (loss) gain for the period										(13.5)	18.1	(142.7)
Amortization of actuarial loss and prior service cost included in net loss										15.4	31.9	32.7
Postretirement plans and workers' compensation obligations										(2.6)	60.4	(98.6)
Foreign currency translation adjustment										(1.8)	(34.9)	(41.0)
Other comprehensive income (loss), net of income taxes										141.9	145.9	(345.6)
Comprehensive loss										(579.5)	(1,812.3)	(1,069.1)
Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest										7.9	7.1	9.7
Comprehensive loss attributable to common stockholders										$ (587.4)	$ (1,819.4)	$ (1,078.8)