Debt - Recourse Debt (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Mar. 31, 2015	Mar. 31, 2016	Mar. 31, 2015
Debt Instrument [Line Items]
Redeemed notes		$ 125
Gain (loss) on extinguishment of debt		$ 4	$ (23)
Unsecured Debt [Member]
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt			$ (23)
Unsecured Debt [Member] | 7.375% Senior Notes Due 2021 [Member] [Member]
Debt Instrument [Line Items]
Interest rate on senior notes		7.375%
Unsecured Debt [Member] | 4.875% Senior Notes Due 2023 [Member] [Member]
Debt Instrument [Line Items]
Interest rate on senior notes		4.875%
Unsecured Debt [Member] | 5.5% Senior Notes Due 2024 [Member] [Member]
Debt Instrument [Line Items]
Interest rate on senior notes		5.50%
Unsecured Debt [Member] | 5.5% Senior Notes Due 2025 [Member] [Member]
Debt Instrument [Line Items]
Interest rate on senior notes		5.50%
Unsecured Debt [Member] | 7.75% Senior Notes Due 2015 [Member]
Debt Instrument [Line Items]
Redeemed notes	$ 151
Interest rate on senior notes	7.75%		7.75%
Unsecured Debt [Member] | 9.75% Senior Notes Due 2016 [Member] [Domain]
Debt Instrument [Line Items]
Redeemed notes	$ 164
Interest rate on senior notes	9.75%		9.75%
Parent Company [Member]
Debt Instrument [Line Items]
Gain (loss) on extinguishment of debt		$ 7