Indebtedness - Summary of Total Indebtedness (Detail) - USD ($) $ in Millions	6 Months Ended	9 Months Ended
Jun. 30, 2020	Sep. 30, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Principal Amount		$ 6,365	$ 5,603
Fair Value of Interest Rate Swap		62	27
Unamortized (Discount) Premium		(24)	(17)
Unamortized Debt Issuance Costs		(40)	(32)
Long term debt		$ 6,363	$ 5,581
4.50% 2012 Senior Notes, due 2022
Debt Instrument [Line Items]
Notes payable, interest rate		4.50%	4.50%
Principal Amount		$ 500	$ 500
Fair Value of Interest Rate Swap		16	9
Unamortized (Discount) Premium		(1)	(1)
Unamortized Debt Issuance Costs		(1)	(1)
Long term debt		$ 514	$ 507
4.875% 2013 Senior Notes, due 2024
Debt Instrument [Line Items]
Notes payable, interest rate		4.875%	4.875%
Principal Amount		$ 500	$ 500
Unamortized (Discount) Premium		(1)	(1)
Unamortized Debt Issuance Costs		(1)	(2)
Long term debt		$ 498	$ 497
5.25% 2014 Senior Notes (30-Year), due 2044
Debt Instrument [Line Items]
Notes payable, interest rate		5.25%	5.25%
Debt instrument, term	30 years	30 years
Principal Amount		$ 600	$ 600
Unamortized (Discount) Premium		4	4
Unamortized Debt Issuance Costs		(5)	(5)
Long term debt		$ 599	$ 599
1.75% 2015 Senior Notes, due 2027
Debt Instrument [Line Items]
Notes payable, interest rate		1.75%	1.75%
Principal Amount		$ 586	$ 561
Unamortized (Discount) Premium			0
Unamortized Debt Issuance Costs			(3)
Long term debt			$ 558
2.75% 2017 Senior Notes, due 2021
Debt Instrument [Line Items]
Notes payable, interest rate		2.75%	2.75%
Principal Amount		$ 586	$ 500
Fair Value of Interest Rate Swap			11
Unamortized (Discount) Premium		0	(1)
Unamortized Debt Issuance Costs		(2)	(2)
Long term debt		$ 584	$ 508
2.625% 2017 Senior Notes, due 2023
Debt Instrument [Line Items]
Notes payable, interest rate		2.625%	2.625%
Principal Amount		$ 500	$ 500
Fair Value of Interest Rate Swap		13	7
Unamortized (Discount) Premium		(1)	(1)
Unamortized Debt Issuance Costs		(2)	(2)
Long term debt		$ 510	$ 504
3.25% 2017 Senior Notes, due 2028
Debt Instrument [Line Items]
Notes payable, interest rate		3.25%	3.25%
Principal Amount		$ 500	$ 500
Fair Value of Interest Rate Swap		34
Unamortized (Discount) Premium		(4)	(4)
Unamortized Debt Issuance Costs		(3)	(3)
Long term debt		$ 527	$ 493
3.25% 2018 Senior Notes, due 2021
Debt Instrument [Line Items]
Notes payable, interest rate		3.25%	3.25%
Principal Amount			$ 300
Unamortized (Discount) Premium			0
Unamortized Debt Issuance Costs			(1)
Long term debt			$ 299
4.25% 2018 Senior Notes, due 2029
Debt Instrument [Line Items]
Notes payable, interest rate		4.25%	4.25%
Principal Amount		$ 400	$ 400
Unamortized (Discount) Premium		(2)	(3)
Unamortized Debt Issuance Costs		(3)	(3)
Long term debt		$ 395	$ 394
4.875% 2018 Senior Notes, due 2048
Debt Instrument [Line Items]
Notes payable, interest rate		4.875%	4.875%
Principal Amount		$ 400	$ 400
Unamortized (Discount) Premium		(7)	(7)
Unamortized Debt Issuance Costs		(4)	(4)
Long term debt		$ 389	$ 389
0.950% Senior Notes Due 2030
Debt Instrument [Line Items]
Notes payable, interest rate		0.95%	0.95%
Principal Amount		$ 879	$ 842
Unamortized (Discount) Premium		(3)	(3)
Unamortized Debt Issuance Costs		(6)	(6)
Long term debt		$ 870	$ 833
3.75% 2020 Senior Notes, due 2025
Debt Instrument [Line Items]
Notes payable, interest rate		3.75%
Debt instrument, term		5 years
Principal Amount		$ 700
Fair Value of Interest Rate Swap		(1)
Unamortized (Discount) Premium		(1)
Unamortized Debt Issuance Costs		(5)
Long term debt		$ 693
3.25% 2020 Senior Notes, due 2050
Debt Instrument [Line Items]
Notes payable, interest rate		3.25%
Debt instrument, term		30 years
Principal Amount		$ 300
Unamortized (Discount) Premium		(4)
Unamortized Debt Issuance Costs		(3)
Long term debt		$ 293
2.55% 2020 Senior Notes, due 2060
Debt Instrument [Line Items]
Notes payable, interest rate		2.55%
Debt instrument, term		40 years
Principal Amount		$ 500
Unamortized (Discount) Premium		(4)
Unamortized Debt Issuance Costs		(5)
Long term debt		$ 491

Face (par) amount of debt instrument at time of issuance.

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