Commitments, Contingencies And Guarantees (External Credit Ratings Of Underlying Or Referenced Assets For Credit Related Derivatives Contracts) (Details) $ in Millions	Sep. 30, 2015 USD ($)
Commitments And Guarantee Obligations [Line Items]
Maximum Payout	$ 6,712.4
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	134.5
AAA/Aaa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	1,746.9
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	22.0
BBB/Baa [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Credit related derivative contracts by external credit ratings	0.0
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	50.6
Notional/Maximum Payout [Member] | Index credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Maximum Payout	1,746.9
Notional/Maximum Payout [Member] | Single name credit default swaps [Member]
Commitments And Guarantee Obligations [Line Items]
Maximum Payout	$ 228.6