Variable Interest Entities - Summary of Consolidated VIE Investment Funds (Details) - USD ($) $ in Millions	9 Months Ended	12 Months Ended
	Sep. 30, 2017	Dec. 31, 2016
Variable Interest Entity [Line Items]
Investment funds	$ 2,670	$ 2,460
Consolidated Entity Excluding Variable Interest Entities (VIE) | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 1,330	$ 1,198
Percent of total	100.00%	100.00%
Consolidated Entity Excluding Variable Interest Entities (VIE) | Private equity | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 396	$ 343
Percent of total	29.80%	28.60%
Consolidated Entity Excluding Variable Interest Entities (VIE) | Private equity – other | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 176	$ 131
Percent of total	13.20%	11.00%
Consolidated Entity Excluding Variable Interest Entities (VIE) | Real estate and other real assets | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 245	$ 247
Percent of total	18.40%	20.60%
Consolidated Entity Excluding Variable Interest Entities (VIE) | Natural resources | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 78	$ 49
Percent of total	5.90%	4.10%
Consolidated Entity Excluding Variable Interest Entities (VIE) | Hedge funds | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 163	$ 192
Percent of total	12.20%	16.00%
Consolidated Entity Excluding Variable Interest Entities (VIE) | Credit funds | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 272	$ 236
Percent of total	20.50%	19.70%
Variable Interest Entities
Variable Interest Entity [Line Items]
Investment funds	$ 593	$ 573
Percent of total	100.00%	100.00%
Variable Interest Entities | Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 583	$ 562
Variable Interest Entities | Private equity
Variable Interest Entity [Line Items]
Investment funds	$ 529	$ 524
Percent of total	89.20%	91.40%
Variable Interest Entities | Real estate and other real assets
Variable Interest Entity [Line Items]
Investment funds	$ 32	$ 11
Percent of total	5.40%	1.90%
Variable Interest Entities | Credit funds
Variable Interest Entity [Line Items]
Investment funds	$ 32	$ 38
Percent of total	5.40%	6.70%
Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party
Variable Interest Entity [Line Items]
Investment funds	$ 747	$ 689
Percent of total	100.00%	100.00%
Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Private equity
Variable Interest Entity [Line Items]
Investment funds	$ 279	$ 268
Percent of total	37.30%	38.90%
Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Real estate and other real assets
Variable Interest Entity [Line Items]
Investment funds	$ 166	$ 118
Percent of total	22.20%	17.20%
Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Natural resources
Variable Interest Entity [Line Items]
Investment funds	$ 5	$ 5
Percent of total	0.70%	0.70%
Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Hedge funds
Variable Interest Entity [Line Items]
Investment funds	$ 62	$ 72
Percent of total	8.30%	10.40%
Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Credit funds
Variable Interest Entity [Line Items]
Investment funds	$ 235	$ 226
Percent of total	31.50%	32.80%
MidCap Holdings | Related Party
Variable Interest Entity [Line Items]
MidCap Investment	$ 767	$ 761
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Private equity | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	3 years	3 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Private equity – other | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	0 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Real estate and other real assets | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	1 year
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Natural resources | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	5 years	5 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Hedge funds | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	9 years	9 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Credit funds | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	1 year	2 years
Minimum | Variable Interest Entities | Real estate and other real assets
Variable Interest Entity [Line Items]
Life of underlying funds	2 years	2 years
Minimum | Variable Interest Entities | Credit funds
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	0 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Private equity
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	0 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Real estate and other real assets
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	0 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Natural resources
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	1 year
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Hedge funds
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	0 years
Minimum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Credit funds
Variable Interest Entity [Line Items]
Life of underlying funds	0 years	0 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Private equity | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	3 years	3 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Private equity – other | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	10 years	10 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Real estate and other real assets | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	7 years	4 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Natural resources | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	8 years	5 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Hedge funds | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	10 years	9 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) | Credit funds | Related Party
Variable Interest Entity [Line Items]
Life of underlying funds	4 years	3 years
Maximum | Variable Interest Entities | Real estate and other real assets
Variable Interest Entity [Line Items]
Life of underlying funds	3 years	3 years
Maximum | Variable Interest Entities | Credit funds
Variable Interest Entity [Line Items]
Life of underlying funds	3 years	3 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Private equity
Variable Interest Entity [Line Items]
Life of underlying funds	7 years	7 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Real estate and other real assets
Variable Interest Entity [Line Items]
Life of underlying funds	6 years	4 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Natural resources
Variable Interest Entity [Line Items]
Life of underlying funds	1 year	2 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Hedge funds
Variable Interest Entity [Line Items]
Life of underlying funds	3 years	3 years
Maximum | Consolidated Entity Excluding Variable Interest Entities (VIE) and Related Party | Credit funds
Variable Interest Entity [Line Items]
Life of underlying funds	5 years	5 years