Segment Information - Reconciliation of Total GAAP Expenses to Segment Expense (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Total expenses	$ 503	$ 422	$ 748
Total expenses	516	431	705
Plus: Credit derivative losses	35	25	27
Operating Segments [Member]
Segment Reporting Information [Line Items]
Total expenses	503	422	748
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Total expenses	25	0	(10)
Plus: Credit derivative losses	$ 13	$ 9	$ (43)