Investments - Schedule of Investments in Unconsolidated Affiliates (Details) - USD ($) $ in Millions		1 Months Ended	3 Months Ended		4 Months Ended
	Mar. 18, 2020	Dec. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Feb. 21, 2020
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates		$ 836.5	$ 759.2		$ 759.2
Equity in losses of unconsolidated affiliates			$ (52.7)	$ (21.4)
Dun & Bradstreet
Schedule of Equity Method Investments [Line Items]
Ownership interest, equity method investment			24.30%		24.30%
Investments in unconsolidated affiliates		385.9	$ 396.5		$ 396.5
Equity in losses of unconsolidated affiliates			10.1	(24.3)
Payments to acquire equity method investments			0.0	502.7
Ceridian
Schedule of Equity Method Investments [Line Items]
Ownership interest, equity method investment						13.70%
Investments in unconsolidated affiliates		$ 309.5	0.0		$ 0.0
Equity in losses of unconsolidated affiliates			$ 1.5	2.6
Equity Fund
Schedule of Equity Method Investments [Line Items]
Ownership interest, equity method investment		49.00%	49.00%		49.00%
Investments in unconsolidated affiliates		$ 46.7	$ 134.3		$ 134.3
Equity in losses of unconsolidated affiliates			(58.8)	0.0
Payments to acquire equity method investments		90.9	$ 101.2		$ 192.1
AmeriLife
Schedule of Equity Method Investments [Line Items]
Ownership interest, equity method investment	20.30%		20.30%		20.30%
Investments in unconsolidated affiliates		0.0	$ 125.0		$ 125.0
Equity in losses of unconsolidated affiliates			0.0	0.0
Payments to acquire equity method investments	$ 125.0
Other
Schedule of Equity Method Investments [Line Items]
Investments in unconsolidated affiliates		$ 94.4	103.4		$ 103.4
Equity in losses of unconsolidated affiliates			$ (5.5)	$ 0.3
Ceridian
Schedule of Equity Method Investments [Line Items]
Equity securities, FV-NI, ownership percentage			13.70%		13.70%