Commitments, Contingencies and Guarantees (Commitments and Contingencies) (Details) $ in Millions	Jun. 30, 2017 USD ($)
Commitments And Guarantee Obligations [Line Items]
2017	$ 7,395.6
2018	436.3
2019 and 2020	361.4
2021 and 2022	92.6
2023 and Later	161.3
Maximum Payout	8,447.2
Equity Commitments [Member]
Commitments And Guarantee Obligations [Line Items]
2017	18.7
2018	33.0
2019 and 2020	12.3
2021 and 2022	0.0
2023 and Later	149.0
Maximum Payout	213.0
Loan Commitments [Member]
Commitments And Guarantee Obligations [Line Items]
2017	54.3
2018	269.4
2019 and 2020	15.6
2021 and 2022	54.9
2023 and Later	0.0
Maximum Payout	394.2
Mortgage-Related And Other Purchase Commitments [Member]
Commitments And Guarantee Obligations [Line Items]
2017	0.0
2018	0.0
2019 and 2020	191.2
2021 and 2022	0.0
2023 and Later	0.0
Maximum Payout	191.2
Forward Starting Reverse Repos [Member]
Commitments And Guarantee Obligations [Line Items]
2017	4,768.1
2018	0.0
2019 and 2020	0.0
2021 and 2022	0.0
2023 and Later	0.0
Maximum Payout	4,768.1
Forward Starting Repos [Member]
Commitments And Guarantee Obligations [Line Items]
2017	2,464.5
2018	0.0
2019 and 2020	0.0
2021 and 2022	0.0
2023 and Later	0.0
Maximum Payout	2,464.5
Other Unfunded Commitments [Member]
Commitments And Guarantee Obligations [Line Items]
2017	90.0
2018	133.9
2019 and 2020	142.3
2021 and 2022	37.7
2023 and Later	12.3
Maximum Payout	$ 416.2