Accumulated Other Comprehensive Income (Loss) - Reclasses Out Of AOCI (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Mar. 31, 2019		Mar. 31, 2018
Accumulated Other Comprehensive Income [Abstract]
Beginning Balance	$ 166.6	$ 338.2	$ 354.8
Other comprehensive income (loss)	3.9	(16.5)	(18.8)
Cumulative effect of change in accounting principle				$ 0.0	[1]	$ 2.2	[2]
Acquisitions of noncontrolling interests		(21.0)
Ending Balance	207.6	166.6	338.2
Benefit plan adjustments
Accumulated Other Comprehensive Income [Abstract]
Beginning Balance	(572.1)	(601.0)	(559.6)
Other comprehensive income (loss) before reclassifications	(33.6)	(22.8)	(78.1)
Amounts reclassified from accumulated other comprehensive loss to net income (loss)	51.5	51.7	36.7
Other comprehensive income (loss)	17.9	28.9	(41.4)
Ending Balance	(583.0)	(572.1)	(601.0)
Foreign Currency Translation Adjustments
Accumulated Other Comprehensive Income [Abstract]
Beginning Balance	(382.0)	(327.4)	(349.1)
Other comprehensive income (loss) before reclassifications	(0.9)	(151.6)	21.7
Amounts reclassified from accumulated other comprehensive loss to net income (loss)	0.1	106.9	0.0
Other comprehensive income (loss)	(0.8)	(44.7)	21.7
Acquisitions of noncontrolling interests		(9.9)
Ending Balance	(382.8)	(382.0)	(327.4)
Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income [Abstract]
Beginning Balance	0.0	1.1	1.0
Other comprehensive income (loss) before reclassifications	0.0	0.0	1.1
Amounts reclassified from accumulated other comprehensive loss to net income (loss)	0.0	0.0	(1.0)
Other comprehensive income (loss)	0.0	0.0	0.1
Ending Balance	0.0	0.0	1.1
Gains (Losses) on Cash Flow Hedges
Accumulated Other Comprehensive Income [Abstract]
Beginning Balance	0.8	0.7	0.7
Other comprehensive income (loss) before reclassifications	(14.0)	0.3	(0.2)
Amounts reclassified from accumulated other comprehensive loss to net income (loss)	0.0	(0.2)	0.2
Other comprehensive income (loss)	(14.0)	0.1	0.0
Ending Balance	(13.2)	0.8	0.7
AOCI Attributable to Parent
Accumulated Other Comprehensive Income [Abstract]
Beginning Balance	(953.3)	(926.6)	(907.0)
Other comprehensive income (loss) before reclassifications	(48.5)	(174.1)	(55.5)
Amounts reclassified from accumulated other comprehensive loss to net income (loss)	51.6	158.4	35.9
Other comprehensive income (loss)	3.1	(15.7)	(19.6)
Cumulative effect of change in accounting principle				(28.8)	[1]	(1.1)	[2]
Acquisitions of noncontrolling interests		(9.9)
Ending Balance	$ (979.0)	$ (953.3)	$ (926.6)
Accounting Standards Update 2016-01 | Unrealized Gains (Losses) on Available-for-Sale Securities
Accumulated Other Comprehensive Income [Abstract]
Cumulative effect of change in accounting principle						(1.1)
Accounting Standards Update 2016-01 | AOCI Attributable to Parent
Accumulated Other Comprehensive Income [Abstract]
Cumulative effect of change in accounting principle						$ (1.1)
Accounting Standards Update 2018-02 | Benefit plan adjustments
Accumulated Other Comprehensive Income [Abstract]
Cumulative effect of change in accounting principle				(28.8)
Accounting Standards Update 2018-02 | AOCI Attributable to Parent
Accumulated Other Comprehensive Income [Abstract]
Cumulative effect of change in accounting principle				$ (28.8)

[1] Effective January 1, 2019, we adopted the provisions of ASU 2018-02, Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income. We recognized a cumulative effect adjustment to January 1, 2019 retained earnings as a result of adopting this standard. See Note 1 for further details.

[2] Effective January 1, 2018, we adopted the provisions of ASU 2014-09, Revenue From Contracts with Customers, ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, and ASU 2016-16, Intra-Entity Transfers of Assets Other Than Inventory. We recognized a cumulative effect adjustment to January 1, 2018 retained earnings as a result of adopting each of these standards. See Note 1 for further details of the impact of each standard.