Fair Value Measurements - Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Millions	Mar. 31, 2021	Mar. 31, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	$ 736	$ 1,401
Equity investments	4,084	2,419
Investments in marketable securities total	4,820	3,820
U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	211	176
Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	10	11
Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	187	197
U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	32	49
Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	1	1
Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	47	45
Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	52	72
Recurring [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	736	1,401
Equity investments	4,084	2,419
Investments in marketable securities total	4,820	3,820
Derivative assets	54	51
Counterparty netting and collateral	(1,302)	(1,386)
Assets at fair value	4,874	3,871
Counterparty netting and collateral	1,384	3,071
Liabilities at fair value	(1)	(45)
Net assets at fair value	4,873	3,826
Recurring [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	196	601
Recurring [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities		249
Recurring [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	211	176
Recurring [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	10	11
Recurring [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	187	197
Recurring [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	32	49
Recurring [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	1	1
Recurring [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	47	45
Recurring [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	52	72
Recurring [Member] | Equity mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	883
Recurring [Member] | Fixed income total return bond funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	2,429	1,673
Recurring [Member] | Counterparty Netting & Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Equity investments	0	0
Investments in marketable securities total	0	0
Derivative assets	(1,302)	(1,386)
Counterparty netting and collateral	(1,302)	(1,386)
Assets at fair value	(1,302)	(1,386)
Counterparty netting and collateral	1,384	3,071
Liabilities at fair value	1,384	3,071
Net assets at fair value	82	1,685
Recurring [Member] | Counterparty Netting & Collateral [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities		0
Recurring [Member] | Counterparty Netting & Collateral [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Equity mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	0
Recurring [Member] | Counterparty Netting & Collateral [Member] | Fixed income total return bond funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	0	0
Recurring [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	330	27
Derivative liabilities	(243)	(1,290)
Recurring [Member] | Foreign currency swaps [Member] | Counterparty Netting & Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Interest rate swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	1,026	1,410
Derivative liabilities	(1,142)	(1,826)
Recurring [Member] | Interest rate swaps [Member] | Counterparty Netting & Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Level 1 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	229	174
Equity investments	3,312	1,673
Investments in marketable securities total	3,541	1,847
Derivative assets	0	0
Counterparty netting and collateral	0	0
Assets at fair value	3,541	1,847
Counterparty netting and collateral	0	0
Liabilities at fair value	0	0
Net assets at fair value	3,541	1,847
Recurring [Member] | Level 1 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	20	0
Recurring [Member] | Level 1 [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities		0
Recurring [Member] | Level 1 [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	209	174
Recurring [Member] | Level 1 [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 1 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 1 [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 1 [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 1 [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 1 [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 1 [Member] | Equity mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	883
Recurring [Member] | Level 1 [Member] | Fixed income total return bond funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	2,429	1,673
Recurring [Member] | Level 1 [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Level 1 [Member] | Interest rate swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Level 2 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	431	1,109
Equity investments	0	0
Investments in marketable securities total	431	1,109
Derivative assets	1,356	1,437
Counterparty netting and collateral	0	0
Assets at fair value	1,787	2,546
Counterparty netting and collateral	0	0
Liabilities at fair value	(1,385)	(3,116)
Net assets at fair value	402	(570)
Recurring [Member] | Level 2 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	176	601
Recurring [Member] | Level 2 [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities		249
Recurring [Member] | Level 2 [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	2	2
Recurring [Member] | Level 2 [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	10	11
Recurring [Member] | Level 2 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	187	197
Recurring [Member] | Level 2 [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	32	49
Recurring [Member] | Level 2 [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 2 [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	5	0
Recurring [Member] | Level 2 [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	19	0
Recurring [Member] | Level 2 [Member] | Equity mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	0
Recurring [Member] | Level 2 [Member] | Fixed income total return bond funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	0	0
Recurring [Member] | Level 2 [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	330	27
Derivative liabilities	(243)	(1,290)
Recurring [Member] | Level 2 [Member] | Interest rate swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	1,026	1,410
Derivative liabilities	(1,142)	(1,826)
Recurring [Member] | Level 3 [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	76	118
Equity investments	0	0
Investments in marketable securities total	76	118
Derivative assets	0	0
Counterparty netting and collateral	0	0
Assets at fair value	76	118
Counterparty netting and collateral	0	0
Liabilities at fair value	0	0
Net assets at fair value	76	118
Recurring [Member] | Level 3 [Member] | Commercial paper [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 3 [Member] | Certificates of deposit [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities		0
Recurring [Member] | Level 3 [Member] | U.S. government and agency obligations [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 3 [Member] | Municipal debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 3 [Member] | Corporate debt securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 3 [Member] | U.S. government agency mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	0	0
Recurring [Member] | Level 3 [Member] | Non-agency residential mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	1	1
Recurring [Member] | Level 3 [Member] | Non-agency commercial mortgage-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	42	45
Recurring [Member] | Level 3 [Member] | Asset-backed securities [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Available-for-sale securities, Debt securities	33	72
Recurring [Member] | Level 3 [Member] | Equity mutual funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	0
Recurring [Member] | Level 3 [Member] | Fixed income total return bond funds [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	0	0
Recurring [Member] | Level 3 [Member] | Foreign currency swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Level 3 [Member] | Interest rate swaps [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Derivative assets	0	0
Derivative liabilities	0	0
Recurring [Member] | Fixed income mutual funds measured at net asset value [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	772	746
Recurring [Member] | Fixed income mutual funds measured at net asset value [Member] | Counterparty Netting & Collateral [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Equity investments	$ 0	$ 0