Debt (Recourse Debt Net Principal Amounts Due Over Five Years) (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017
Debt Details [Line Items]
Recourse Debt Total	$ 3,655	$ 4,630
Unamortized (discounts)/premiums & debt issuance (costs)
Debt Details [Line Items]
Recourse Debt Total	(31)
Parent Company [Member]
Debt Details [Line Items]
Recourse Debt Total	3,655
Parent Company [Member] | 2018
Debt Details [Line Items]
Recourse Debt Total	5
Parent Company [Member] | 2019
Debt Details [Line Items]
Recourse Debt Total	5
Parent Company [Member] | 2020
Debt Details [Line Items]
Recourse Debt Total	505
Parent Company [Member] | 2021
Debt Details [Line Items]
Recourse Debt Total	350
Parent Company [Member] | 2022
Debt Details [Line Items]
Recourse Debt Total	1,213
Parent Company [Member] | Thereafter
Debt Details [Line Items]
Recourse Debt Total	1,608
Parent Company [Member] | Unamortized (discounts)/premiums & debt issuance (costs)
Debt Details [Line Items]
Recourse Debt Total	$ (31)	$ (40)