Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 97	$ 88
Net realized and unrealized (gains)/losses	39	(19)
Transfers out of Level 3 to Level 2	(2)	(1)
Balance as of the end of the period	$ 134	$ 70