Supplemental Cash Flow Information - Reconciliation of Cash, Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Millions	Sep. 30, 2018	Dec. 31, 2017	Sep. 30, 2017	Dec. 31, 2016
Supplemental Cash Flow Elements [Abstract]
Cash and cash equivalents	$ 939.0	$ 405.6	$ 207.2	$ 382.3
Restricted cash recorded in prepaid expenses and other current assets	58.2	62.3	64.6	42.5
Total cash, cash equivalents and restricted cash shown in the statements of cash flows	$ 997.2	$ 467.9	$ 271.8	$ 424.8