Derivative Financial Instruments (Notional Amounts, Balance Sheet Location And Estimated Fair Values Of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Derivative [Line Items]
Contractual notional amount	$ 23,224.1	$ 13,778.4
Total derivative assets	329.7	529.8
Amounts netted	(170.6)	(216.7)
Net derivative assets	159.1	313.1
Total derivative liabilities	(430.0)	(477.1)
Amounts netted	170.6	216.7
Net derivative liabilities	(259.4)	(260.4)
Hedging Instruments [Member]
Derivative [Line Items]
Contractual notional amount	1,385.0	1,185.0
Hedging Instruments [Member] | Other Assets/Other Liabilities
Derivative [Line Items]
Contractual notional amount	6,035.0
Total derivative assets	22.7
Total derivative liabilities	(91.7)
Hedging Instruments [Member] | Other Assets/Other Liabilities | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual notional amount	1,385.0	1,185.0
Total derivative assets	7.0	2.6
Total derivative liabilities	(0.8)	(7.8)
Hedging Instruments [Member] | Other Assets/Other Liabilities | Forward Contracts [Member]
Derivative [Line Items]
Contractual notional amount	4,650.0
Total derivative assets	15.7
Total derivative liabilities	(90.9)
Non-Hedging Instruments [Member]
Derivative [Line Items]
Contractual notional amount	17,189.1	12,593.4
Total derivative assets	307.0	527.2
Total derivative liabilities	(338.3)	(469.3)
Non-Hedging Instruments [Member] | Other Assets/Other Liabilities | Options [Member]
Derivative [Line Items]
Contractual notional amount	16,917.4	12,208.5
Total derivative assets	305.7	428.0
Total derivative liabilities	(332.1)	(458.4)
Non-Hedging Instruments [Member] | Fixed Maturity Securities [Member] | Derivatives Embedded In Convertible Fixed Maturity Securities [Member]
Derivative [Line Items]
Contractual notional amount		287.0
Total derivative assets		98.7
Total derivative liabilities		0.0
Non-Hedging Instruments [Member] | Equity Securities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual notional amount	271.7	97.9
Total derivative assets	1.2	0.0
Total derivative liabilities	(6.0)	(9.4)
Non-Hedging Instruments [Member] | Equity Securities [Member] | Futures [Member]
Derivative [Line Items]
Contractual notional amount	0.0	0.0
Total derivative assets	0.1	0.5
Total derivative liabilities	$ (0.2)	$ (1.5)