Fair Value of Financial Instruments Unobservable Input Reconciliation (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance as of the beginning of the period	$ 72	$ 129	$ 88	$ 139
Net realized and unrealized (gains)/losses	30	(2)	14	(10)
Transfers out of Level 3 to Level 2	(1)	(2)	(1)	(4)
Balance as of the end of the period	$ 101	$ 125	$ 101	$ 125