Summary of Significant Accounting Policies - Cumulative Effect of Adjustments to the Condensed Consolidated Balance Sheets (Details) - USD ($) $ in Millions	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Assets:
Prepaid expenses and other current assets	$ 306.1	$ 266.7	$ 268.1
Property and equipment, net	848.7	908.8	951.7
Operating lease assets	171.9	192.5
Other long-term assets	430.4	404.8	403.5
Total assets	8,753.6	9,512.8	9,363.3
Liabilities:
Other accrued liabilities	275.4	269.1	233.5
Long-term operating lease liabilities	163.5	185.5
Other long-term liabilities	58.1	53.1	119.8
Total liabilities	4,111.2	4,694.5	4,540.1
Stockholders' Equity:
Accumulated deficit	$ (2,832.7)	(2,836.3)	$ (2,831.4)
Accounting Standards Update 2016-02
Assets:
Prepaid expenses and other current assets		(1.4)
Property and equipment, net		(42.9)
Operating lease assets		192.5
Other long-term assets		1.3
Total assets		149.5
Liabilities:
Other accrued liabilities		35.6
Long-term operating lease liabilities		185.5
Other long-term liabilities		(66.7)
Total liabilities		154.4
Stockholders' Equity:
Accumulated deficit		$ (4.9)