Balance Sheet Accounts - Schedule of Changes in Accumulated Other Comprehensive Loss by Components, Net of Income Taxes (Details) $ in Millions	6 Months Ended
	Jun. 30, 2017 USD ($)
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (303.0)
Amortization of actuarial losses and prior service credits, net of $12.4 million of income taxes	19.1
Ending balance	(283.9)
Defined Benefit Plans Adjustment
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income, tax benefit	12.4
Actuarial Losses, Net
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(303.2)
Amortization of actuarial losses and prior service credits, net of $12.4 million of income taxes	19.1
Ending balance	(284.1)
Prior Service Credits, Net
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	0.2
Amortization of actuarial losses and prior service credits, net of $12.4 million of income taxes	0.0
Ending balance	$ 0.2