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Loans Payable, Long-Term Debt and Leases - Long-Term Debt (Details) - USD ($) $ in Millions	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term debt	$ 22,736		$ 19,806
2.75% notes due 2025
Debt Instrument [Line Items]
Long-term debt	$ 2,492		2,490
Stated interest rate (as percent)	2.75%
3.70% notes due 2045
Debt Instrument [Line Items]
Long-term debt	$ 1,975		1,974
Stated interest rate (as percent)	3.70%
2.80% notes due 2023
Debt Instrument [Line Items]
Long-term debt	$ 1,747		1,745
Stated interest rate (as percent)	2.80%
3.40% notes due 2029
Debt Instrument [Line Items]
Long-term debt	$ 1,732		0
Stated interest rate (as percent)	3.40%	3.40%
4.00% notes due 2049
Debt Instrument [Line Items]
Long-term debt	$ 1,468		0
Stated interest rate (as percent)	4.00%	4.00%
2.35% notes due 2022
Debt Instrument [Line Items]
Long-term debt	$ 1,248		1,214
Stated interest rate (as percent)	2.35%
4.15% notes due 2043
Debt Instrument [Line Items]
Long-term debt	$ 1,238		1,237
Stated interest rate (as percent)	4.15%
3.875% notes due 2021
Debt Instrument [Line Items]
Long-term debt	$ 1,151		1,132
Stated interest rate (as percent)	3.875%
1.125% euro-denominated notes due 2021
Debt Instrument [Line Items]
Long-term debt	$ 1,113		1,134
Stated interest rate (as percent)	1.125%
1.875% euro-denominated notes due 2026
Debt Instrument [Line Items]
Long-term debt	$ 1,107		1,127
Stated interest rate (as percent)	1.875%
2.40% notes due 2022
Debt Instrument [Line Items]
Long-term debt	$ 1,010		983
Stated interest rate (as percent)	2.40%
3.90% notes due 2039
Debt Instrument [Line Items]
Long-term debt	$ 982		0
Stated interest rate (as percent)	3.90%	3.90%
2.90% notes due 2024
Debt Instrument [Line Items]
Long-term debt	$ 745		0
Stated interest rate (as percent)	2.90%	2.90%
6.50% notes due 2033
Debt Instrument [Line Items]
Long-term debt	$ 722		726
Stated interest rate (as percent)	6.50%
0.50% euro-denominated notes due 2024
Debt Instrument [Line Items]
Long-term debt	$ 555		565
Stated interest rate (as percent)	0.50%
1.375% euro-denominated notes due 2036
Debt Instrument [Line Items]
Long-term debt	$ 551		561
Stated interest rate (as percent)	1.375%
2.50% euro-denominated notes due 2034
Debt Instrument [Line Items]
Long-term debt	$ 550		560
Stated interest rate (as percent)	2.50%
3.60% notes due 2042
Debt Instrument [Line Items]
Long-term debt	$ 490		490
Stated interest rate (as percent)	3.60%
6.55% notes due 2037
Debt Instrument [Line Items]
Long-term debt	$ 412		414
Stated interest rate (as percent)	6.55%
5.75% notes due 2036
Debt Instrument [Line Items]
Long-term debt	$ 338		338
Stated interest rate (as percent)	5.75%
5.95% debentures due 2028
Debt Instrument [Line Items]
Long-term debt	$ 306		306
Stated interest rate (as percent)	5.95%
5.85% notes due 2039
Debt Instrument [Line Items]
Long-term debt	$ 271		270
Stated interest rate (as percent)	5.85%
6.40% debentures due 2028
Debt Instrument [Line Items]
Long-term debt	$ 250		250
Stated interest rate (as percent)	6.40%
6.30% debentures due 2026
Debt Instrument [Line Items]
Long-term debt	$ 135		135
Stated interest rate (as percent)	6.30%
1.85% notes due 2020
Debt Instrument [Line Items]
Long-term debt	$ 0		$ 1,231
Stated interest rate (as percent)			1.85%
Floating-rate notes due 2020
Debt Instrument [Line Items]
Long-term debt	0		$ 699
Other
Debt Instrument [Line Items]
Long-term debt	$ 148		$ 225

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