Debt, Description of long-term debt (Details) - USD ($) $ in Millions	1 Months Ended		6 Months Ended
	Apr. 30, 2020	Mar. 31, 2020	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Long-term debt [Line Items]
Issuance of long-term debt			$ 2,492
Outstanding borrowings			13,677		$ 11,617
Repayments of long-term debt			500	$ 1,000
Senior Revolving Credit Facility due 2022, $2,500 million [Member]
Long-term debt [Line Items]
Maximum borrowing capacity			$ 2,500
Expiration date			June 2022
Maximum allowed letters of credit			$ 500
Additional borrowing capacity, uncommitted loans			$ 1,000
Description of interest rate			Borrowings under the facility bear interest at either a base rate or LIBOR rate, plus an applicable margin. Additional fees are incurred for the average daily unused commitments.
Issuance of long-term debt		$ 500
Outstanding borrowings			$ 0
Outstanding letters of credit			0
Unused availability			2,017
Repayments of long-term debt	$ 500
Guaranteed notes due 2025, 2.875% [Member]
Long-term debt [Line Items]
Outstanding borrowings			496
Face amount	$ 500		$ 500
Interest rate	2.875%		2.875%
Maturity year	2025		2025
Discounted prices at which long-term debt was issued (in thousandths)	99.911%
Guaranteed notes due 2030, 3.375% [Member]
Long-term debt [Line Items]
Outstanding borrowings			$ 495
Face amount	$ 500		$ 500
Interest rate	3.375%		3.375%
Maturity year	2030		2030
Discounted prices at which long-term debt was issued (in thousandths)	99.813%
Guaranteed notes due 2050, 4.2% [Member]
Long-term debt [Line Items]
Outstanding borrowings			$ 984
Face amount	$ 1,000		$ 1,000
Interest rate	4.20%		4.20%
Maturity year	2050		2050
Discounted prices at which long-term debt was issued (in thousandths)	99.373%
Guaranteed notes due 2025, 2030 and 2050 [Member]
Long-term debt [Line Items]
Issuance of long-term debt	$ 1,974
Issuance date	April 2020
Description of debt redemption terms	The 2025 Notes, 2030 Notes and 2050 Notes may be redeemed before the date that is one month, three months, or six months, respectively, prior to the scheduled maturity date at a redemption price equal to the greater of 100% of the principal amount of the notes redeemed and the sum of the present values of the remaining scheduled payments of principal and interest (discounted at the applicable treasury yield plus 40 basis points in the case of the 2025 Notes or 45 basis points in the case of the 2030 Notes and 2050 Notes) on the notes to be redeemed. The 2025 Notes, 2030 Notes and 2050 Notes may also be redeemed on or after the date that is one month, three months, or six months, respectively, prior to the scheduled maturity date of the notes at a redemption price equal to 100% of the principal amount of the notes redeemed plus accrued and unpaid interest. The notes are also redeemable upon certain tax events.