Investments - Investment Segment (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Schedule of Investments [Line Items]
Investments	$ 9,498		$ 9,498		$ 9,945
Securities sold, not yet purchased, at fair value	1,819		1,819		1,190
Investment Segment
Schedule of Investments [Line Items]
Investments	8,681		8,681		9,207
Securities sold, not yet purchased, at fair value	1,819		1,819		1,190
Unrealized gain (loss) on debt and equity securities still held	2,566	$ (118)	(1,066)	$ 434
Investment Segment | Equity securities:
Schedule of Investments [Line Items]
Investments	8,583		8,583		9,062
Investment Segment | Basic materials
Schedule of Investments [Line Items]
Investments					281
Securities sold, not yet purchased, at fair value					209
Investment Segment | Consumer, non-cyclical
Schedule of Investments [Line Items]
Investments	1,724		1,724		2,085
Securities sold, not yet purchased, at fair value	716		716		29
Investment Segment | Consumer, cyclical
Schedule of Investments [Line Items]
Investments	3,037		3,037		2,427
Securities sold, not yet purchased, at fair value	831		831		379
Investment Segment | Energy
Schedule of Investments [Line Items]
Investments	2,634		2,634		1,717
Securities sold, not yet purchased, at fair value	123		123		124
Investment Segment | Financial
Schedule of Investments [Line Items]
Securities sold, not yet purchased, at fair value					152
Investment Segment | Technology
Schedule of Investments [Line Items]
Investments	1,115		1,115		2,425
Securities sold, not yet purchased, at fair value	149		149		217
Investment Segment | Industrial
Schedule of Investments [Line Items]
Investments	73		73		127
Investment Segment | Communication
Schedule of Investments [Line Items]
Securities sold, not yet purchased, at fair value					80
Investment Segment | Corporate debt securities
Schedule of Investments [Line Items]
Investments	$ 98		$ 98		$ 145