Derivative Financial Instruments (Notional Amounts, Balance Sheet Location And Estimated Fair Values Of Derivative Financial Instruments) (Details) - USD ($) $ in Millions	Sep. 30, 2017	Dec. 31, 2016
Derivative [Line Items]
Contractual Notional Amount	$ 6,263.1	$ 16,834.9
Total derivative assets	7.2	758.7
Amounts netted	(7.2)	(92.8)
Net derivative assets	0.0	665.9
Total derivative liabilities	(79.9)	(241.9)
Amounts netted	79.9	92.8
Net derivative liabilities	0.0	(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	5,610.0	6,160.0
Total derivative assets	4.8	532.8
Total derivative liabilities	(79.3)	(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	0.8	4.0
Total derivative liabilities	(3.6)	(0.7)
Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Forward Contracts [Member]
Derivative [Line Items]
Contractual Notional Amount	4,375.0	4,775.0
Total derivative assets	4.0	528.8
Total derivative liabilities	(75.7)	(6.0)
Non-Hedging Instrument [Member]
Derivative [Line Items]
Contractual Notional Amount	653.1	10,674.9
Total derivative assets	2.4	225.9
Total derivative liabilities	(0.6)	(235.2)
Non-Hedging Instrument [Member] | Other Assets/Other Liabilities [Member] | Options [Member]
Derivative [Line Items]
Contractual Notional Amount	200.0	10,280.2
Total derivative assets	0.0	220.7
Total derivative liabilities	0.0	(233.9)
Non-Hedging Instrument [Member] | Equity Securities [Member] | Interest Rate Swaps [Member]
Derivative [Line Items]
Contractual Notional Amount	342.5	209.4
Total derivative assets	0.9	4.7
Total derivative liabilities	(0.3)	(0.2)
Non-Hedging Instrument [Member] | Equity Securities [Member] | Futures [Member]
Derivative [Line Items]
Contractual Notional Amount	110.6	185.3
Total derivative assets	1.5	0.5
Total derivative liabilities	$ (0.3)	$ (1.1)