Derivative Financial Instruments (Notional Amounts, Balance Sheet Location And Estimated Fair Values Of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Derivative [Line Items]
Contractual notional amount	$ 16,834.9	$ 23,376.1
Total derivative assets	758.7	329.7
Amounts netted	(92.8)	(170.6)
Net derivative assets	665.9	159.1
Total derivative liabilities	(241.9)	(430.0)
Amounts netted	92.8	170.6
Net derivative liabilities	(149.1)	(259.4)
Hedging Instruments [Member]
Derivative [Line Items]
Contractual notional amount	1,385.0	1,385.0
Hedging Instruments [Member] | Other Assets/Other Liabilities
Derivative [Line Items]
Contractual notional amount	6,160.0	6,035.0
Total derivative assets	532.8	22.7
Total derivative liabilities	(6.7)	(91.7)
Hedging Instruments [Member] | Other Assets/Other Liabilities | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual notional amount	1,385.0	1,385.0
Total derivative assets	4.0	7.0
Total derivative liabilities	(0.7)	(0.8)
Hedging Instruments [Member] | Other Assets/Other Liabilities | Forward Contracts [Member]
Derivative [Line Items]
Contractual notional amount	4,775.0	4,650.0
Total derivative assets	528.8	15.7
Total derivative liabilities	(6.0)	(90.9)
Non-Hedging Instruments [Member]
Derivative [Line Items]
Contractual notional amount	10,674.9	17,341.1
Total derivative assets	225.9	307.0
Total derivative liabilities	(235.2)	(338.3)
Non-Hedging Instruments [Member] | Other Assets/Other Liabilities | Options [Member]
Derivative [Line Items]
Contractual notional amount	10,280.2	16,917.4
Total derivative assets	220.7	305.7
Total derivative liabilities	(233.9)	(332.1)
Non-Hedging Instruments [Member] | Equity Securities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual notional amount	209.4	271.7
Total derivative assets	4.7	1.2
Total derivative liabilities	(0.2)	(6.0)
Non-Hedging Instruments [Member] | Equity Securities [Member] | Futures [Member]
Derivative [Line Items]
Contractual notional amount	185.3	152.0
Total derivative assets	0.5	0.1
Total derivative liabilities	$ (1.1)	$ (0.2)