Fair Value Measurements (Summary of Assets and Liabilities at Fair Value) (Schedule) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Assets:
Derivative instruments:	$ 3,078.3	$ 1,827.5
SMAs	1,974.0
Other investments	800.3
Total investments	2,774.3	1,289.2
Total assets	5,852.6	3,116.7
Liabilities:
Derivative instruments:	1,343.8	1,582.7
Debt	43.6	45.6
Total liabilities	1,387.4	1,628.3
Quoted prices in active markets for identical assets (Level 1)
Assets:
Derivative instruments:	0.0	0.0
SMAs	520.3
Other investments	364.8
Total investments	885.1	869.2
Total assets	885.1	869.2
Liabilities:
Derivative instruments:	0.0	0.0
Debt	0.0	0.0
Total liabilities	0.0	0.0
Significant other observable inputs (Level 2)
Assets:
Derivative instruments:	2,024.6	1,164.1
SMAs	1,453.7
Other investments	0.0
Total investments	1,453.7	0.0
Total assets	3,478.3	1,164.1
Liabilities:
Derivative instruments:	1,332.1	1,562.8
Debt	43.6	45.6
Total liabilities	1,375.7	1,608.4
Significant unobservable inputs (Level 3)
Assets:
Derivative instruments:	1,053.7	663.4
SMAs	0.0
Other investments	435.5
Total investments	435.5	420.0
Total assets	1,489.2	1,083.4
Liabilities:
Derivative instruments:	11.7	19.9
Debt	0.0	0.0
Total liabilities	11.7	19.9
Cross-currency and interest rate derivative contracts
Assets:
Derivative instruments:	2,019.4	1,157.2
Liabilities:
Derivative instruments:	1,341.8	1,581.5
Cross-currency and interest rate derivative contracts | Quoted prices in active markets for identical assets (Level 1)
Assets:
Derivative instruments:	0.0	0.0
Liabilities:
Derivative instruments:	0.0	0.0
Cross-currency and interest rate derivative contracts | Significant other observable inputs (Level 2)
Assets:
Derivative instruments:	2,019.4	1,157.2
Liabilities:
Derivative instruments:	1,330.1	1,561.6
Cross-currency and interest rate derivative contracts | Significant unobservable inputs (Level 3)
Assets:
Derivative instruments:	0.0	0.0
Liabilities:
Derivative instruments:	11.7	19.9
Equity-related derivative instruments
Assets:
Derivative instruments:	1,053.7	663.4
Equity-related derivative instruments | Quoted prices in active markets for identical assets (Level 1)
Assets:
Derivative instruments:	0.0	0.0
Equity-related derivative instruments | Significant other observable inputs (Level 2)
Assets:
Derivative instruments:	0.0	0.0
Equity-related derivative instruments | Significant unobservable inputs (Level 3)
Assets:
Derivative instruments:	1,053.7	663.4
Foreign currency forward and option contracts
Assets:
Derivative instruments:	5.1	6.0
Liabilities:
Derivative instruments:	1.6	1.2
Foreign currency forward and option contracts | Quoted prices in active markets for identical assets (Level 1)
Assets:
Derivative instruments:	0.0	0.0
Liabilities:
Derivative instruments:	0.0	0.0
Foreign currency forward and option contracts | Significant other observable inputs (Level 2)
Assets:
Derivative instruments:	5.1	6.0
Liabilities:
Derivative instruments:	1.6	1.2
Foreign currency forward and option contracts | Significant unobservable inputs (Level 3)
Assets:
Derivative instruments:	0.0	0.0
Liabilities:
Derivative instruments:	0.0	0.0
Other
Assets:
Derivative instruments:	0.1	0.9
Liabilities:
Derivative instruments:	0.4	0.0
Other | Quoted prices in active markets for identical assets (Level 1)
Assets:
Derivative instruments:	0.0	0.0
Liabilities:
Derivative instruments:	0.0
Other | Significant other observable inputs (Level 2)
Assets:
Derivative instruments:	0.1	0.9
Liabilities:
Derivative instruments:	0.4
Other | Significant unobservable inputs (Level 3)
Assets:
Derivative instruments:	0.0	$ 0.0
Liabilities:
Derivative instruments:	$ 0.0