Borrowings - Interest on Debt (Details) - USD ($) $ in Millions	9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017
Interest on Debt
Interest capitalized	$ 3
Interest capitalized		$ (1)
Total interest paid and accrued	1,101	947
Cost of financing
Interest on Debt
Interest paid	568	496
Interest expense
Interest on Debt
Interest paid	$ 530	$ 451