Fair Value (Carrying and Fair Value By Level of Financial Instruments Not Recorded At Fair Value On Consolidated Balance Sheet) (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	$ 1,542.6	$ 1,387.6
Short-term borrowings	400.0	250.0
Commercial paper	379.2	570.9
Convertible debentures	966.0
Carrying Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	1,542.6	1,387.7
Short-term borrowings	400.0	250.0
Commercial paper	379.2	570.9
Notes	12,746.4	13,198.9
Convertible debentures	966.0	958.1
Estimated Fair Value [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Other invested assets, long-term	1,542.6	1,387.7
Short-term borrowings	400.0	250.0
Commercial paper	379.2	570.9
Notes	13,014.3	14,407.1
Convertible debentures	2,030.6	1,613.4
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
Short-term borrowings	0	0
Commercial paper	0	0
Notes	0	0
Convertible debentures	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
Short-term borrowings	400.0	250.0
Commercial paper	379.2	570.9
Notes	13,014.3	14,407.1
Convertible debentures	2,030.6	1,613.4
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	1,542.6	1,387.7
Short-term borrowings	0	0
Commercial paper	0	0
Notes	0	0
Convertible debentures	$ 0	$ 0