Related Parties - Management Fees Incurred (Details) - Related Party - Asset management fees - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Related Party Transaction [Line Items]
Due to related parties	$ 72		$ 72		$ 54
Expenses from transactions with related parties	$ 94	$ 86	$ 186	$ 169