Commitments, Contingencies And Guarantees (External Credit Ratings Of Underlying Or Referenced Assets For Credit Related Derivatives Contracts) (Details) $ in Millions	Mar. 31, 2016 USD ($)
Commitments And Guarantee Obligations [Line Items]
Maximum Payout	$ 3,656.2
Below Investment Grade [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
Below Investment Grade [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	164.6
AAA/Aaa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	3.5
AAA/Aaa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
AA/Aa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
AA/Aa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
A [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
A [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
BBB/Baa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	49.0
BBB/Baa [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	21.5
Unrated [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
Unrated [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	51.1
Notional/Maximum Payout [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Maximum Payout	52.5
Notional/Maximum Payout [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Maximum Payout	$ 237.2