Derivative Financial Instruments (Notional Amounts, Balance Sheet Location And Estimated Fair Values Of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016
Derivative [Line Items]
Contractual Notional Amount	$ 19,564.0	$ 16,834.9
Total derivative assets	321.2	758.7
Amounts netted	(162.9)	(92.8)
Net derivative assets	158.3	665.9
Total derivative liabilities	(332.9)	(241.9)
Amounts netted	162.9	92.8
Net derivative liabilities	(170.0)	(149.1)
Hedging Instrument [Member]
Derivative [Line Items]
Contractual Notional Amount	1,235.0	1,385.0
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member]
Derivative [Line Items]
Contractual Notional Amount	6,010.0	6,160.0
Total derivative assets	1.0	532.8
Total derivative liabilities	(17.4)	(6.7)
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual Notional Amount	1,235.0	1,385.0
Total derivative assets	1.0	4.0
Total derivative liabilities	(4.8)	(0.7)
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Forward Contracts [Member]
Derivative [Line Items]
Contractual Notional Amount	4,775.0	4,775.0
Total derivative assets	0.0	528.8
Total derivative liabilities	(12.6)	(6.0)
Non-Hedging Instrument [Member]
Derivative [Line Items]
Contractual Notional Amount	13,554.0	10,674.9
Total derivative assets	320.2	225.9
Total derivative liabilities	(315.5)	(235.2)
Non-Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Options [Member]
Derivative [Line Items]
Contractual Notional Amount	13,234.5	10,280.2
Total derivative assets	315.2	220.7
Total derivative liabilities	(315.0)	(233.9)
Non-Hedging Instrument [Member] | Equity Securities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual Notional Amount	126.8	209.4
Total derivative assets	4.4	4.7
Total derivative liabilities	0.0	(0.2)
Non-Hedging Instrument [Member] | Equity Securities [Member] | Futures [Member]
Derivative [Line Items]
Contractual Notional Amount	192.7	185.3
Total derivative assets	0.6	0.5
Total derivative liabilities	$ (0.5)	$ (1.1)