Supplemental Financial Data - Other Income (Expense) - Net (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended				12 Months Ended
	Feb. 07, 2019		Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2020	Dec. 31, 2019		Dec. 31, 2018
Disclosure Text Block Supplement [Abstract]
Non-operating pension income (expense)	$ (85.7)						$ 45.9	$ 35.9		$ (2.4)
Change in fair value of make-whole derivative liability	0.0			$ (102.6)	$ 69.8	$ (172.4)	(32.8)	(172.4)		0.0
Other nonoperating expense related to partial debt redemption	0.0		$ (25.5)	$ (41.3)			(50.1)	0.0		0.0
Miscellaneous other income (expense) – Net	(0.3)						25.0	(18.3)		(0.9)
Other income (expense) – net	(86.0)	[1]					(12.0)	(154.8)	[1]	(3.3)
Pension settlement charge	$ 85.8						$ 0.6	$ 0.0		$ 0.0

[1] See Note 1 "Basis of Presentation" for further discussion.