Assets and Liabilities Measured at Fair Value - Realized and Unrealized Gains (Losses) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Realized and unrealized gains (losses) on financial instruments
Realized and unrealized gains (losses) on financial instruments, net	$ 23	$ (113)	$ (115)	$ (194)
Gain (loss) on changes in fair value	(90)	10	129	(19)
Cumulative amount of gain (loss) in change in fair value	301		301
Equity securities
Realized and unrealized gains (losses) on financial instruments
Realized and unrealized gains (losses) on financial instruments, net		(3)	(4)	2
Exchangeable senior debentures
Realized and unrealized gains (losses) on financial instruments
Realized and unrealized gains (losses) on financial instruments, net	(30)	(139)	(80)	(255)
Indemnification asset
Realized and unrealized gains (losses) on financial instruments
Realized and unrealized gains (losses) on financial instruments, net	35	23	13	55
Other Financial Instruments
Realized and unrealized gains (losses) on financial instruments
Realized and unrealized gains (losses) on financial instruments, net	$ 18	$ 6	$ (44)	$ 4