Long-Term Debt and Available Credit Facilities Available Committed Credit Facilities (Narrative) (Details) $ in Millions	36 Months Ended	37 Months Ended	60 Months Ended
	Nov. 13, 2021	Mar. 31, 2019	Nov. 13, 2023	Dec. 31, 2020 USD ($)	Nov. 13, 2018 USD ($)	Mar. 22, 2016 USD ($)	May 31, 2014 USD ($)
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				$ 6,000
Line of Credit Facility, Remaining Borrowing Capacity				6,000
Revolving Credit Facilities due 2024 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				3,000	$ 3,000
Line of Credit Facility, Remaining Borrowing Capacity				3,000
Debt Instrument, Term			5 years
Revolving Credit Facilities due 2022 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity				3,000	$ 3,000
Line of Credit Facility, Remaining Borrowing Capacity				$ 3,000
Debt Instrument, Term	3 years
Revolving Credit Facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity							$ 3,000
Term Loan Facility due 2020 [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity						$ 4,500
Debt Instrument, Term		3 years
Revolving Credit Facilities due 2022 [Member]
Line of Credit Facility [Line Items]
Ratio of Indebtedness to Net Capital					0.60