Short-Term Debt (Details) - USD ($) $ in Millions	3 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
Short-term Debt [Line Items]
Amount outstanding at period end	$ 1,410	$ 595
Commercial Paper
Short-term Debt [Line Items]
Borrowing limit	4,300	3,600
Amount outstanding at period end	1,410	595
Average amount outstanding	1,496	1,115
Maximum amount outstanding	$ 1,770	$ 1,780
Weighted average interest rate, computed on a daily basis	1.65%	2.72%
Weighted average interest rate at period end	0.76%	2.34%