Fair Value (Carrying And Estimated Fair Values by Level Of Financial Instruments Not Recorded At Fair Value On Consolidated Balance Sheet) (Details) (USD $) In Millions, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other invested assets, long-term	$ 1,516.8	$ 1,387.7
Short-term borrowings	350.0	250.0
Commercial paper	794.9
Level I [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [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
Level II [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other invested assets, long-term	0	0
Short-term borrowings	350.0	250.0
Commercial paper	794.9	570.9
Notes	13,071.5	14,407.1
Convertible debentures	1,909.7	1,613.4
Level III [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other invested assets, long-term	1,516.8	1,387.7
Short-term borrowings	0	0
Commercial paper	0	0
Notes	0	0
Convertible debentures	0	0
Total [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other invested assets, long-term	1,516.8	1,387.7
Short-term borrowings	350.0	250.0
Commercial paper	794.9	570.9
Notes	13,071.5	14,407.1
Convertible debentures	1,909.7	1,613.4
Carrying Value [Member]
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Other invested assets, long-term	1,516.8	1,387.7
Short-term borrowings	350.0	250.0
Commercial paper	794.9	570.9
Notes	12,755.1	13,198.9
Convertible debentures	$ 964.0	$ 958.1