Borrowings - Interest on Debt (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
Interest on Debt
Interest capitalized	$ 3	$ 0
Total interest paid and accrued	349	293
Cost of Financing
Interest on Debt
Interest paid	182	158
Interest Expense
Interest on Debt
Interest paid	$ 165	$ 135