Derivative Financial Instruments (Notional Amounts, Balance Sheet Location And Estimated Fair Values Of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2016	Dec. 31, 2015
Derivative [Line Items]
Contractual Notional Amount	$ 20,308.2	$ 23,376.1
Total derivative assets	280.2	329.7
Amounts netted	(119.2)	(170.6)
Net derivative assets	161.0	159.1
Total derivative liabilities	(269.9)	(430.0)
Amounts netted	119.2	170.6
Net derivative liabilities	(150.7)	(259.4)
Hedging Instrument [Member]
Derivative [Line Items]
Contractual Notional Amount	1,385.0	1,385.0
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member]
Derivative [Line Items]
Contractual Notional Amount	6,160.0	6,035.0
Total derivative assets	36.7	22.7
Total derivative liabilities	(4.0)	(91.7)
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual Notional Amount	1,385.0	1,385.0
Total derivative assets	16.4	7.0
Total derivative liabilities	(0.9)	(0.8)
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Forward Contracts [Member]
Derivative [Line Items]
Contractual Notional Amount	4,775.0	4,650.0
Total derivative assets	20.3	15.7
Total derivative liabilities	(3.1)	(90.9)
Non-Hedging Instrument [Member]
Derivative [Line Items]
Contractual Notional Amount	14,148.2	17,341.1
Total derivative assets	243.5	307.0
Total derivative liabilities	(265.9)	(338.3)
Non-Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Options [Member]
Derivative [Line Items]
Contractual Notional Amount	13,776.8	16,917.4
Total derivative assets	243.1	305.7
Total derivative liabilities	(244.5)	(332.1)
Non-Hedging Instrument [Member] | Equity Securities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual Notional Amount	269.6	271.7
Total derivative assets	0.0	1.2
Total derivative liabilities	(21.2)	(6.0)
Non-Hedging Instrument [Member] | Equity Securities [Member] | Futures [Member]
Derivative [Line Items]
Contractual Notional Amount	101.8	152.0
Total derivative assets	0.4	0.1
Total derivative liabilities	$ (0.2)	$ (0.2)