Restructuring (Rollforward of Restructuring Liability) (Details) - USD ($) $ in Millions	3 Months Ended			6 Months Ended			12 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Jun. 30, 2020	Jun. 30, 2021	Dec. 31, 2020	Jun. 30, 2020	Jun. 30, 2021
Restructuring Cost and Reserve [Line Items]
Total charges	$ 20.1		$ 0.0	$ 50.1		$ 0.0
Restructuring Reserve [Roll Forward]
Balance as of beginning of period	27.1	$ 44.5		44.5	$ 0.0		$ 0.0
Accrued charges	15.9	23.9			94.1
Payments	(24.7)	(41.3)			(49.6)
Balance as of end of period	18.3	27.1	0.0	18.3	44.5	0.0	18.3
Total non-cash charges				10.3	24.9		35.2
Cumulative charges incurred through June 30, 2021	169.1			169.1			169.1
Minimum
Restructuring Cost and Reserve [Line Items]
Estimated restructuring expenses remaining	80.0			80.0			80.0
Maximum
Restructuring Cost and Reserve [Line Items]
Estimated restructuring expenses remaining	$ 105.0			$ 105.0			$ 105.0
Employee Compensation
Restructuring Cost and Reserve [Line Items]
Estimated restructuring expenses remaining (percent)	40.00%			40.00%			40.00%
Restructuring Reserve [Roll Forward]
Balance as of beginning of period	$ 24.1	44.5		$ 44.5	0.0		$ 0.0
Accrued charges	12.8	19.8			85.0
Payments	(20.4)	(40.2)			(40.5)
Balance as of end of period	16.5	24.1	0.0	16.5	44.5	0.0	16.5
Total non-cash charges				7.5	19.5		27.0
Cumulative charges incurred through June 30, 2021	144.6			144.6			144.6
Other Expenses
Restructuring Reserve [Roll Forward]
Balance as of beginning of period	3.0	0.0		0.0	0.0		0.0
Accrued charges	3.1	4.1			9.1
Payments	(4.3)	(1.1)			(9.1)
Balance as of end of period	1.8	$ 3.0	$ 0.0	1.8	0.0	$ 0.0	1.8
Total non-cash charges				2.8	$ 5.4		8.2
Cumulative charges incurred through June 30, 2021	$ 24.5			$ 24.5			$ 24.5