Debt (Schedule of Debt) (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Commercial paper	$ 312	$ 699
Short-term bank borrowings	200	0
Carrying value of senior debt	17,980	17,980
Obligations under finance leases	43	44
Total debt	18,537	18,719
Less current portion of long-term debt	20	18
Total long-term debt, net of current portion	18,005	18,002
Net unamortized discount on senior debt	406	412
Unamortized deferred financing costs	90	92
Decrease (increase) in the carrying value of debt relating to previously settled fair value hedges	6	6
Face value of debt	19,040	19,230
4.30% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 300	300
Stated interest rate	4.30%
4.50% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 499	499
Stated interest rate	4.50%
3.875% Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 598	597
Stated interest rate	3.875%
2.250% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 49	49
Stated interest rate	2.25%
3.375% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 698	698
Stated interest rate	3.375%
3.125% Senior Notes due 2022 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 194	194
Stated interest rate	3.125%
2.50% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 398	398
Stated interest rate	2.50%
3.25% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 181	181
Stated interest rate	3.25%
2.90% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 397	396
Stated interest rate	2.90%
4.25% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 1,242	1,242
Stated interest rate	4.25%
7.875% Debentures due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 187	187
Stated interest rate	7.875%
7.125% Senior Notes due 2023 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 46	46
Stated interest rate	7.125%
3.875% Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 489	489
Stated interest rate	3.875%
3.70% Senior Notes due 2024 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 598	598
Stated interest rate	3.70%
3.50% Senior Notes due 2025 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 592	592
Stated interest rate	3.50%
4.00% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 789	789
Stated interest rate	4.00%
3.45% Senior Notes due 2026 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 123	123
Stated interest rate	3.45%
2.90% Senior Notes due 2027 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 688	688
Stated interest rate	2.90%
3.375% Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 494	494
Stated interest rate	3.375%
3.70% Senior Notes due 2028 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 491	491
Stated interest rate	3.70%
4.20% Senior Notes due 2029 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 493	493
Stated interest rate	4.20%
7.875% Senior Debentures due 2030 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 831	831
Stated interest rate	7.875%
5.50% Senior Debentures due 2033 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 426	426
Stated interest rate	5.50%
4.85% Senior Debentures due 2034 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 87	87
Stated interest rate	4.85%
6.875% Senior Debentures due 2036 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 1,069	1,068
Stated interest rate	6.875%
6.75% Senior Debentures due 2037 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 75	75
Stated interest rate	6.75%
5.90% Senior Notes due 2040 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 297	297
Stated interest rate	5.90%
4.50% Senior Debentures due 2042 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 45	45
Stated interest rate	4.50%
4.85% Senior Notes due 2042 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 487	486
Stated interest rate	4.85%
4.375% Senior Debentures due 2043 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 1,111	1,109
Stated interest rate	4.375%
4.875% Senior Debentures due 2043 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 18	18
Stated interest rate	4.875%
5.850% Senior Debentures due 2043 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 1,231	1,231
Stated interest rate	5.85%
5.25% Senior Debentures due 2044 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 345	345
Stated interest rate	5.25%
4.90% Senior Notes due 2044 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 539	539
Stated interest rate	4.90%
4.60% Senior Notes due 2045 [Member]
Debt Instrument [Line Items]
Carrying value of senior debt	$ 589	589
Stated interest rate	4.60%
5.875% Junior Subordinated Debentures due 2057 [Member]
Debt Instrument [Line Items]
Junior Subordinated Notes	$ 643	643
Stated interest rate	5.875%
6.25% Junior Subordinated Debentures due 2057 [Member]
Debt Instrument [Line Items]
Junior Subordinated Notes	$ 643	$ 643
Stated interest rate	6.25%

Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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