Fair Value Measurement - Financial Assets Measured at Fair Value (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	$ 21,083.2	$ 22,049.3	$ 21,783.6	$ 21,864.1
Transfers in				4.5
Transfers out	(115.1)	(47.7)	(119.0)	(135.2)
Purchases	3,271.4	2,841.9	7,041.5	7,190.7
Sales	(2,071.6)	(1,045.0)	(4,934.5)	(3,658.2)
Settlements	(1,195.6)	(1,054.2)	(2,693.1)	(3,285.7)
Realized and unrealized gains (losses), net
Included in earnings	(101.1)	193.5	978.4	923.1
Included in other comprehensive income	160.0	(685.0)	(1,025.7)	(650.5)
Balance, end of period	21,031.2	22,252.8	21,031.2	22,252.8
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	(320.7)	46.7	(67.0)	87.0
Equity securities
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,023.8	2,582.4	1,968.5	2,714.1
Transfers in				4.5
Transfers out	(115.1)	(47.7)	(115.1)	(135.2)
Purchases	32.6	1.1	60.6	27.5
Sales	(21.0)	(4.1)	(1,043.3)	(430.6)
Settlements	0.0	0.0	0.0	0.0
Realized and unrealized gains (losses), net
Included in earnings	11.1	44.0	261.0	389.7
Included in other comprehensive income	24.6	(190.2)	(175.7)	(184.5)
Balance, end of period	956.0	2,385.5	956.0	2,385.5
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	3.3	55.5	(299.2)	81.8
Bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	1,193.7	1,345.8	1,235.8	1,249.5
Transfers in				0.0
Transfers out	0.0	0.0	0.0	0.0
Purchases	177.8	167.2	403.2	557.2
Sales	(117.1)	(180.5)	(324.9)	(486.2)
Settlements	0.0	0.0	0.0	0.0
Realized and unrealized gains (losses), net
Included in earnings	(27.7)	(2.8)	(4.4)	14.4
Included in other comprehensive income	2.5	(80.9)	(80.5)	(86.1)
Balance, end of period	1,229.2	1,248.8	1,229.2	1,248.8
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	(24.9)	(3.0)	(4.9)	9.3
Loans
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	15,460.9	14,344.7	15,084.9	14,067.8
Transfers in				0.0
Transfers out	0.0	0.0	0.0	0.0
Purchases	2,948.7	2,572.3	6,223.0	6,331.7
Sales	(1,543.2)	(607.3)	(2,682.1)	(1,805.4)
Settlements	(1,195.6)	(1,054.2)	(2,693.1)	(3,285.7)
Realized and unrealized gains (losses), net
Included in earnings	(204.7)	(47.0)	(88.3)	(65.9)
Included in other comprehensive income	16.1	(391.3)	(362.2)	(425.3)
Balance, end of period	15,482.2	14,817.2	15,482.2	14,817.2
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	(199.8)	(50.0)	(112.7)	(36.3)
Partnership and LLC interests
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	3,390.1	3,761.8	3,481.0	3,815.2
Transfers in				0.0
Transfers out	0.0	0.0	0.0	0.0
Purchases	112.3	101.3	350.8	274.3
Sales	(390.3)	(252.1)	(884.2)	(931.4)
Settlements	0.0	0.0	0.0	0.0
Realized and unrealized gains (losses), net
Included in earnings	121.3	199.8	809.8	584.7
Included in other comprehensive income	116.8	(22.5)	(407.2)	45.5
Balance, end of period	3,350.2	3,788.3	3,350.2	3,788.3
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	(98.5)	44.7	349.2	31.6
Other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	4.0	1.5	1.5	2.0
Transfers in				0.0
Transfers out	0.0	0.0	0.0	0.0
Purchases	0.0	0.0	0.0	0.0
Sales	0.0	(0.8)	0.0	(0.8)
Settlements	0.0	0.0	0.0	0.0
Realized and unrealized gains (losses), net
Included in earnings	(0.7)	0.2	1.9	(0.3)
Included in other comprehensive income	0.0	(0.1)	(0.1)	(0.1)
Balance, end of period	3.3	0.8	3.3	0.8
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	(0.7)	0.2	2.1	0.1
Trading securities and other
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	2.0	4.7	3.3	6.9
Transfers in				0.0
Transfers out	0.0	0.0	0.0	0.0
Purchases	0.0	0.0	0.0	0.0
Sales	0.0	(0.2)	0.0	(3.8)
Settlements	0.0	0.0	0.0	0.0
Realized and unrealized gains (losses), net
Included in earnings	(0.4)	(0.8)	(1.7)	0.6
Included in other comprehensive income	0.0	0.0	0.0	0.0
Balance, end of period	1.6	3.7	1.6	3.7
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	(0.1)	(0.8)	(1.4)	0.6
Restricted securities of Consolidated Funds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Balance, beginning of period	8.7	8.4	8.6	8.6
Transfers in				0.0
Transfers out	0.0	0.0	(3.9)	0.0
Purchases	0.0	0.0	3.9	0.0
Sales	0.0	0.0	0.0	0.0
Settlements	0.0	0.0	0.0	0.0
Realized and unrealized gains (losses), net
Included in earnings	0.0	0.1	0.1	(0.1)
Included in other comprehensive income	0.0	0.0	0.0	0.0
Balance, end of period	8.7	8.5	8.7	8.5
Changes in unrealized gains (losses) included in earnings related to financial assets still held at the reporting date	$ 0.0	$ 0.1	$ (0.1)	$ (0.1)