Schedule of New Accounting Pronouncements (Details) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014	Dec. 31, 2013
New Accounting Pronouncements or Change in Accounting Principle
Other Long-term Investments	$ 603.1	$ 530.8	$ 545.0
Deferred Income Tax	173.3	300.7	62.0
Retained Earnings	7,472.9	8,251.5	7,302.3
Net Investment Income	602.0	615.8
Current Income Tax	40.6	37.8
Deferred Income Tax	49.5	66.2
Net Income	212.9	225.8
Basic Earnings Per Share	$ 0.85	$ 0.87
Diluted Earnings Per Share	$ 0.84	$ 0.86
Change in Income Taxes	161.4	142.9
Non-cash Components of Net Investment Income	(90.5)	(100.0)
Previously Reported Amount
New Accounting Pronouncements or Change in Accounting Principle
Other Long-term Investments		565.0	591.9
Deferred Income Tax		312.6	78.4
Retained Earnings		8,273.8	7,332.8
Net Investment Income		612.5
Current Income Tax		29.7
Deferred Income Tax		67.9
Net Income		228.9
Basic Earnings Per Share		$ 0.88
Diluted Earnings Per Share		$ 0.88
Change in Income Taxes		136.5
Non-cash Components of Net Investment Income		(96.7)
Accounting Standards Update 2014-01 | Restatement Adjustment
New Accounting Pronouncements or Change in Accounting Principle
Other Long-term Investments		(34.2)	(46.9)
Deferred Income Tax		(11.9)	(16.4)
Retained Earnings		(22.3)	(30.5)	19.2
Net Investment Income		3.3
Current Income Tax		8.1
Deferred Income Tax		(1.7)
Net Income		(3.1)
Basic Earnings Per Share		$ (0.01)
Diluted Earnings Per Share		$ (0.02)
Change in Income Taxes		6.4
Non-cash Components of Net Investment Income		$ (3.3)