Borrowings Under Credit Facilities and Commercial Paper Program - Narrative (Details)	1 Months Ended	6 Months Ended
	Jan. 31, 2019 USD ($)	Jun. 30, 2021 USD ($) bank term	Dec. 31, 2020 USD ($)	[1]
Line of Credit Facility [Line Items]
Number of banks in consortium | bank		34
Borrowings outstanding		$ 0	$ 0
Unsecured revolving credit facility
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		4,000,000,000
Borrowings outstanding		$ 0
Number of successive terms | term		2
Successive term		6 months
Available to borrow in alternate currencies		$ 1,000,000,000
Facility fee		0.15%
Unsecured revolving credit facility | Credit Facility, Tranche Due 2023
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		$ 1,000,000,000
Unsecured revolving credit facility | Credit Facility, Tranche Due 2025
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		$ 3,000,000,000
Unsecured revolving credit facility | LIBOR
Line of Credit Facility [Line Items]
Interest rate margin		0.775%
Unsecured revolving credit facility | Accordion feature
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		$ 1,250,000,000
Term credit facility
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		500,000,000
Term credit facility, CAD denominated
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		250,000,000
Term credit facility, CAD denominated | Accordion feature
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement		250,000,000
Commercial paper note program
Line of Credit Facility [Line Items]
Unsecured line of credit arrangement	$ 1,000,000,000
Borrowings outstanding		$ 0
Commercial paper note program | Maximum
Line of Credit Facility [Line Items]
Debt instrument, term	397 days

[1] Note: The consolidated balance sheet at December 31, 2020 has been derived from the audited financial statements at that date but does not include all of the information and footnotes required by U.S. generally accepted accounting principles for complete financial statements.