Indebtedness - Principal Payments Due on Long-Term Borrowings (Detail) - USD ($) $ in Millions	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
2021 (After June 30,)	$ 0
2022	500
2023	500
2024	500
2025	700
Thereafter	4,182
Total principal payment	6,382	$ 6,430
4.50% 2012 Senior Notes, due 2022
Debt Instrument [Line Items]
2022	500
Total principal payment	500	500
4.875% 2013 Senior Notes, due 2024
Debt Instrument [Line Items]
2024	500
Total principal payment	500	500
5.25% 2014 Senior Notes, due 2044
Debt Instrument [Line Items]
Thereafter	600
Total principal payment	600	600
1.75% 2015 Senior Notes, due 2027
Debt Instrument [Line Items]
Thereafter	593
Total principal payment	593	612
2.625% 2017 Senior Notes, due 2023
Debt Instrument [Line Items]
2023	500
Total principal payment	500	500
3.25% 2017 Senior Notes, due 2028
Debt Instrument [Line Items]
Thereafter	500
Total principal payment	500	500
4.25% 2018 Senior Notes, due 2029
Debt Instrument [Line Items]
Thereafter	400
Total principal payment	400	400
4.875% 2018 Senior Notes, due 2048
Debt Instrument [Line Items]
Thereafter	400
Total principal payment	400	400
0.950% Senior Notes Due 2030
Debt Instrument [Line Items]
Thereafter	889
Total principal payment	889	918
3.75% 2020 Senior Notes, due 2025
Debt Instrument [Line Items]
2025	700
Total principal payment	700	700
3.25% 2020 Senior Notes, due 2050
Debt Instrument [Line Items]
Thereafter	300
Total principal payment	300	300
2.55% 2020 Senior Notes, due 2060
Debt Instrument [Line Items]
Thereafter	500
Total principal payment	$ 500	$ 500

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