Borrowing and Lines of Credit (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Line of Credit Facility [Line Items]
Maximum Commercial Paper Borrowing Authority	$ 5,000
Aggregate Line of Credit Agreements, Maximum Borrowing Capacity	7,000
Borrowings outstanding	0
Proceeds from Issuance of Debt	$ 0
Average Years of Maturity of Long Term Debt	14 years
Average interest expense rate	4.10%	3.80%
5.0B Revolving Credit Agreement [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 5,000
$2.0B May 6, 2020 revolving credit agreement [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	$ 2,000