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Debt and Financing Activities - Long-Term Debt (Details) |  | 12 Months Ended
--- | --- | ---
Nov. 30, 2018 USD ($) | Mar. 31, 2020 USD ($) | Mar. 31, 2020 EUR (€) | Mar. 31, 2019 USD ($) | Mar. 31, 2018 USD ($) | Mar. 31, 2018 EUR (€)
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 7,387,000,000 |  | $ 7,595,000,000 |  |
Proceeds from issuances of long-term debt |  | 0 |  | 1,099,000,000 | $ 1,522,000,000 |
Pre-tax loss on debt extinguishment |  | 0 |  | 0 | 122,000,000 |
Repayments of long-term debt |  | 298,000,000 |  | 1,112,000,000 | 2,287,000,000 |
Scheduled principal payments of long-term debt in 2021 |  | 1,100,000,000 |  |  |  |
Scheduled principal payments of long-term debt in 2022 |  | 704,000,000 |  |  |  |
Scheduled principal payments of long-term debt in 2023 |  | 813,000,000 |  |  |  |
Scheduled principal payments of long-term debt in 2024 |  | 1,100,000,000 |  |  |  |
Scheduled principal payments of long-term debt in 2025 |  | 16,000,000 |  |  |  |
Scheduled principal payments of long-term debt, thereafter |  | 3,700,000,000 |  |  |  |
3.65% Notes due November 30, 2020 | Notes Payable |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt interest rate (percent) | 3.65% |  |  |  |  |
Aggregate principal amount | $ 700,000,000 |  |  |  |  |
3.65% Notes due November 30, 2020 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 700,000,000 |  | 700,000,000 |  |
Debt interest rate (percent) |  | 3.65% |  |  |  |
Notes Due November 30, 2020 and Notes Due May 30, 2029 | Notes Payable |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Proceeds from issuances of long-term debt | $ 1,100,000,000 |  |  |  |  |
Redemption price (percent) |  | 101.00% | 101.00% |  |  |
4.75% Notes due May 30, 2029 | Notes Payable |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt interest rate (percent) | 4.75% |  |  |  |  |
Aggregate principal amount | $ 400,000,000 |  |  |  |  |
4.75% Notes due May 30, 2029 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 400,000,000 |  | 400,000,000 |  |
Debt interest rate (percent) |  | 4.75% |  |  |  |
Notes and Debentures Extinguished February 7, 2018 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Aggregate consideration of debt paid to redeem debt |  |  |  |  | 1,400,000,000 |
Debt redeemed |  |  |  |  | 1,200,000,000 |
Debt premiums |  |  |  |  | 112,000,000 |
Unpaid interest |  |  |  |  | 22,000,000 |
Pre-tax loss on debt extinguishment |  |  |  |  | 122,000,000 |
After-tax loss on debt extinguishment |  |  |  |  | $ 78,000,000 |
7.50% Notes due February 15, 2019 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt interest rate (percent) |  |  |  |  | 7.50% |
4.75% Notes due March 1, 2021 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 323,000,000 |  | 323,000,000 |  |
Debt interest rate (percent) |  | 4.75% |  |  | 4.75% |
7.65% Debentures due March 1, 2027 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 167,000,000 |  | 167,000,000 |  |
Debt interest rate (percent) |  | 7.65% |  |  | 7.65% |
6.00% Notes due March 1, 2041 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 282,000,000 |  | 282,000,000 |  |
Debt interest rate (percent) |  | 6.00% |  |  | 6.00% |
4.88% Notes due March 15, 2044 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 411,000,000 |  | 411,000,000 |  |
Debt interest rate (percent) |  | 4.88% |  |  | 4.88% |
Floating Rate Euro Notes due February 12, 2020 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 0 |  | $ 280,000,000 |  |
Repayments of long-term debt | € |  |  | € 250,000,000 |  |  |
4.50% Euro Bonds due April 26, 2017 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt interest rate (percent) |  |  |  |  | 4.50% |
Repayments of long-term debt | € |  |  |  |  |  | € 500,000,000
1.40% Notes due March 15, 2018 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt interest rate (percent) |  |  |  |  | 1.40% |
Repayments of long-term debt |  |  |  |  | $ 500,000,000 |
2.28% Notes due March 15, 2019 | Notes |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Debt interest rate (percent) |  |  |  | 2.28% |  |
Repayments of long-term debt |  |  |  | $ 1,100,000,000 |  |
Long-term Debt, Current Maturities |  |  |  |  |  |
Debt Instrument [Line Items] |  |  |  |  |  |
Total debt outstanding |  | $ 1,100,000,000 |  | $ 330,000,000 |  |

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