Fair Value (Carrying and Fair Value By Level of Financial Instruments Not Recorded At Fair Value On Consolidated Balance Sheet) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	$ 2,041.1	$ 1,695.9
Convertible debentures	330.7
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	2,041.1	1,695.9
Short-term borrowings	540.0	400.0
Commercial paper	682.2
Notes	14,311.6	13,777.8
Convertible debentures	330.7	974.4
Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	2,041.1	1,695.9
Short-term borrowings	540.0	400.0
Commercial paper	682.2
Notes	14,523.2	14,794.8
Convertible debentures	980.1	2,581.9
Estimated Fair Value [Member] | Level I [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	0.0	0.0
Short-term borrowings	0.0	0.0
Commercial paper	0.0
Notes	0.0	0.0
Convertible debentures	0.0	0.0
Estimated Fair Value [Member] | Level II [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	0.0	0.0
Short-term borrowings	540.0	400.0
Commercial paper	682.2
Notes	14,523.2	14,794.8
Convertible debentures	980.1	2,581.9
Estimated Fair Value [Member] | Level III [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	2,041.1	1,695.9
Short-term borrowings	0.0	0.0
Commercial paper	0.0
Notes	0.0	0.0
Convertible debentures	$ 0.0	$ 0.0