Supplemental Cash Flow Information - Adoption of Accounting Standards (Details) $ in Millions	12 Months Ended
	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