Debt Senior Unsecured Notes (Details) - USD ($) $ in Millions	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Long-term Debt	$ 11,682	$ 11,292
Senior Unsecured Notes 2023 [Member]
Debt Instrument [Line Items]
Long-term Debt	1,236	1,235
Senior Unsecured Notes 2024 [Member]
Debt Instrument [Line Items]
Long-term Debt	642	641
Senior Unsecured Notes 2025 [Member]
Debt Instrument [Line Items]
Long-term Debt	1,531	1,530
Unsecured Debt [Member]
Debt Instrument [Line Items]
Long-term Debt	$ 3,409	$ 3,406