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Supplemental Cash Flow Information - Adoption of Accounting Standards (Details) $ in Millions | 12 Months Ended
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Dec. 31, 2018 USD ($) Provisions | Dec. 31, 2017 USD ($) | Dec. 31, 2016 USD ($)
Operating activities |  |  |
Other current assets | $ (10.0) | $ (7.1) | $ 103.2
Other, net | 290.4 | (197.4) | (53.6)
Net cash provided by operating activities |  | 2,078.6 | 2,103.8
Investing activities |  |  |
Withdrawal of restricted cash from rabbi trust for qualifying payments |  | 0.0 | 0.0
Proceeds from the sale of investments held in rabbi trust | 118.6 | 8.7 | 1.7
Purchase of investments held in rabbi trust |  | (3.7) | (59.2)
Net cash used in investing activities |  | (2,254.1) | (1,354.2)
Net change in cash, cash equivalents, and restricted cash | 87.5 | (14.1) | (96.1)
Cash, cash equivalents, and restricted cash at beginning of year | 58.6 | 72.7 | 168.8
Cash, cash equivalents, and restricted cash at end of year | 146.1 | 58.6 | 72.7
2017 Form 10-K Cash Flows |  |  |
Operating activities |  |  |
Other current assets |  | (6.0) | 103.1
Other, net |  | (197.5) | (53.8)
Net cash provided by operating activities |  | 2,079.6 | 2,103.5
Investing activities |  |  |
Withdrawal of restricted cash from rabbi trust for qualifying payments |  | 19.5 | 26.6
Proceeds from the sale of investments held in rabbi trust |  | 0.0 | 0.0
Purchase of investments held in rabbi trust |  | 0.0 | 0.0
Net cash used in investing activities |  | (2,239.6) | (1,270.1)
Net change in cash, cash equivalents, and restricted cash |  | 1.4 | (12.3)
Cash, cash equivalents, and restricted cash at beginning of year | 38.9 | 37.5 | 49.8
Cash, cash equivalents, and restricted cash at end of year |  | 38.9 | 37.5
Accounting Standards Update 2016-18 | Impact of ASU |  |  |
Operating activities |  |  |
Other current assets |  | (1.1) | 0.1
Other, net |  | 0.1 | 0.2
Net cash provided by operating activities |  | (1.0) | 0.3
Investing activities |  |  |
Withdrawal of restricted cash from rabbi trust for qualifying payments |  | (19.5) | (26.6)
Proceeds from the sale of investments held in rabbi trust |  | 8.7 | 1.7
Purchase of investments held in rabbi trust |  | (3.7) | (59.2)
Net cash used in investing activities |  | (14.5) | (84.1)
Net change in cash, cash equivalents, and restricted cash |  | (15.5) | (83.8)
Cash, cash equivalents, and restricted cash at beginning of year | $ 19.7 | 35.2 | 119.0
Cash, cash equivalents, and restricted cash at end of year |  | 19.7 | 35.2
Accounting Standards Update 2016-15 |  |  |
Adoption of ASU 2016-15 |  |  |
Number of provisions in ASU 2016-15 | Provisions | 8 |  |
Impact on financial statements from adoption | $ 0.0 | $ 0.0 | $ 0.0

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