Schedule of New Accounting Pronouncements (Details) - USD ($) $ / shares in Units, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014	Dec. 31, 2013
Consolidated Statements of Income
Net Investment Income	$ 630.7	$ 632.4	$ 1,232.7	$ 1,248.2
Current Income Tax	105.9	86.6	146.5	124.4
Deferred Income Tax	(10.4)	23.8	39.1	90.0
Net Income	$ 224.3	$ 239.4	$ 437.2	$ 465.2
Basic Earnings Per Share	$ 0.90	$ 0.93	$ 1.75	$ 1.80
Diluted Earnings Per Share	$ 0.90	$ 0.93	$ 1.74	$ 1.79
Consolidated Statements of Cash Flows
Change in Income Taxes			$ 141.2	$ 169.8
Non-cash Components of Net Investment Income			(195.4)	(190.2)
Consolidated Balance Sheets
Other Long-term Investments	$ 585.0	$ 531.8	585.0	531.8	$ 545.0
Deferred Income Tax	41.2	406.1	41.2	406.1	62.0
Retained Earnings	$ 7,656.0	8,453.5	$ 7,656.0	8,453.5	7,302.3
Previously Reported Amount
Consolidated Statements of Income
Net Investment Income		629.1		1,241.6
Current Income Tax		78.6		108.3
Deferred Income Tax		25.4		93.3
Net Income		$ 242.5		$ 471.4
Basic Earnings Per Share		$ 0.94		$ 1.83
Diluted Earnings Per Share		$ 0.94		$ 1.82
Consolidated Statements of Cash Flows
Change in Income Taxes				$ 157.0
Non-cash Components of Net Investment Income				(183.6)
Consolidated Balance Sheets
Other Long-term Investments		$ 570.8		570.8	591.9
Deferred Income Tax		419.7		419.7	78.4
Retained Earnings		8,478.9		8,478.9	7,332.8
Accounting Standards Update 2014-01 | Restatement Adjustment
Consolidated Statements of Income
Net Investment Income		3.3		6.6
Current Income Tax		8.0		16.1
Deferred Income Tax		(1.6)		(3.3)
Net Income		$ (3.1)		$ (6.2)
Basic Earnings Per Share		$ (0.01)		$ (0.03)
Diluted Earnings Per Share		$ (0.01)		$ (0.03)
Consolidated Statements of Cash Flows
Change in Income Taxes				$ 12.8
Non-cash Components of Net Investment Income				(6.6)
Consolidated Balance Sheets
Other Long-term Investments		$ (39.0)		(39.0)	(46.9)
Deferred Income Tax		(13.6)		(13.6)	(16.4)
Retained Earnings		$ (25.4)		$ (25.4)	$ (30.5)	$ 19.2