Consolidated Statements Of Stockholders' Equity - USD ($) shares in Thousands, $ in Millions	Total	Common Stock	Additional Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance (in shares) at Mar. 31, 2017		308,367
Beginning balance at Mar. 31, 2017	$ 4,060	$ 3	$ 1,049	$ 3,027	$ (19)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	(107)
Amounts reclassified from accumulated other comprehensive income (loss)	(1)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	935			1,043	(108)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	242		242
Stock Issued During Period, Shares, New Issues		3,332
Stock Issued During Period, Value, New Issues	(42)		(42)
Stock Repurchased and Retired During Period, Shares		(5,329)
Stock Repurchased and Retired During Period, Value	(601)		(601)
Ending balance (in shares) at Mar. 31, 2018		306,370
Ending balance at Mar. 31, 2018	4,595	$ 3	657	4,062	(127)
Beginning balance (in shares) at Mar. 31, 2018		306,370
Beginning balance at Mar. 31, 2018	4,595	$ 3	657	4,062	(127)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	81
Other comprehensive income (loss) before reclassifications | Accounting Standards Update 2014-09 [Member]					22
Amounts reclassified from accumulated other comprehensive income (loss)	(7)
Amounts reclassified from accumulated other comprehensive income (loss) | Accounting Standards Update 2018-02 [Member]					1
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	1,093			1,019	74
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	284		284
Stock Issued During Period, Shares, New Issues		2,722
Stock Issued During Period, Value, New Issues	(61)		(61)
Stock Repurchased and Retired During Period, Shares		(10,985)
Stock Repurchased and Retired During Period, Value	$ (1,192)		(880)	(312)
Ending balance (in shares) at Mar. 31, 2019	298,000	298,107
Ending balance at Mar. 31, 2019	$ 5,331	$ 3	0	5,358	(30)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2014-09 [Member]	612			590
Cumulative Effect of New Accounting Principle in Period of Adoption | Accounting Standards Update 2018-02 [Member]				(1)
Other comprehensive income (loss) before reclassifications	44
Amounts reclassified from accumulated other comprehensive income (loss)	(64)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	3,019			3,039	(20)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	347		347
Stock Issued During Period, Shares, New Issues		2,623
Stock Issued During Period, Value, New Issues	(29)		(29)
Stock Repurchased and Retired During Period, Shares		(12,317)
Stock Repurchased and Retired During Period, Value	$ (1,207)		(318)	(889)
Ending balance (in shares) at Mar. 31, 2020	288,000	288,413
Ending balance at Mar. 31, 2020	$ 7,461	$ 3	$ 0	$ 7,508	$ (50)