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