Borrowings - Outstanding Borrowings (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2021	Mar. 09, 2021	Dec. 31, 2020
Outstanding Borrowings
Total borrowings at par value			$ 2,870.0		$ 3,080.0
Debt issuance costs and unamortized discount, net			(17.4)		(12.8)
Total borrowings at carrying value			$ 2,852.6		3,067.2
Weighted-average effective interest rate (as a percent)			3.40%
Repayment of long-term debt			$ 1,150.0
Commercial paper
Outstanding Borrowings
Total borrowings at par value			120.0		80.0
Maximum borrowing capacity			$ 1,500.0
Maximum days to maturity			397 days
Weighted-average effective interest rate (as a percent)			0.20%
Weighted-average term			1 day
3.600% notes due 2022
Outstanding Borrowings
Total borrowings at par value					$ 500.0
Stated interest rate (as a percent)	3.60%				3.60%
Repayment of long-term debt	$ 500.0
4.250% notes due 2023
Outstanding Borrowings
Total borrowings at par value			$ 300.0		$ 300.0
Stated interest rate (as a percent)			4.25%		4.25%
2.850% notes due 2025
Outstanding Borrowings
Total borrowings at par value			$ 500.0		$ 500.0
Stated interest rate (as a percent)			2.85%		2.85%
1.350% notes due 2026
Outstanding Borrowings
Total borrowings at par value		$ 600.0	$ 600.0	$ 600.0
Stated interest rate (as a percent)		1.35%	1.35%
Effective interest rate (as a percent)			1.50%
2.750% notes due 2031
Outstanding Borrowings
Total borrowings at par value			$ 300.0	$ 300.0
Stated interest rate (as a percent)			2.75%	2.75%
Effective interest rate (as a percent)			2.90%
6.200% notes due 2036
Outstanding Borrowings
Total borrowings at par value			$ 500.0		$ 500.0
Stated interest rate (as a percent)			6.20%		6.20%
6.200% notes due 2040
Outstanding Borrowings
Total borrowings at par value			$ 250.0		$ 250.0
Stated interest rate (as a percent)			6.20%		6.20%
Term loan facility borrowing (effective rate of 3.0%)
Outstanding Borrowings
Total borrowings at par value			$ 300.0		$ 950.0
Effective interest rate (as a percent)			1.40%
Repayment of long-term debt		$ 650.0