Condensed Consolidated Statements of Stockholders' Equity Statement - 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, 2018			306,370
Beginning balance at Mar. 31, 2018	$ 4,595		$ 3	$ 657	$ 4,062	$ (127)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Cumulative Effect on Retained Earnings, Net of Tax | Accounting Standards Update 2014-09 [Member]					590
Cumulative Effect on Retained Earnings, Net of Tax | ASU 2018-02 [Member]					(1)
Other comprehensive income (loss) before reclassifications | Accounting Standards Update 2014-09 [Member]						22
Amounts reclassified from accumulated other comprehensive income (loss) | ASU 2018-02 [Member]						1
Cumulative Effect on Retained Earnings, Tax | Accounting Standards Update 2014-09 [Member]	612
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	371				293	78
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	70			70
Stock Issued During Period, Shares, New Issues			1,280
Stock Issued During Period, Value, New Issues	(88)			(88)
Stock Repurchased and Retired During Period, Shares			(2,264)
Stock Repurchased and Retired During Period, Value	(300)			(300)	0
Ending balance (in shares) at Jun. 30, 2018			305,386
Ending balance at Jun. 30, 2018	5,260		$ 3	339	4,944	(26)
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
Amounts reclassified from accumulated other comprehensive income (loss)	6
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 897
Stock Repurchased and Retired During Period, Shares	(600)
Stock Repurchased and Retired During Period, Value	$ (76)
Ending balance (in shares) at Dec. 31, 2018			300,894
Ending balance at Dec. 31, 2018	5,344		$ 3	0	5,358	(17)
Beginning balance (in shares) at Jun. 30, 2018			305,386
Beginning balance at Jun. 30, 2018	5,260		$ 3	339	4,944	(26)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	262				255	7
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	66			66
Stock Issued During Period, Shares, New Issues			618
Stock Issued During Period, Value, New Issues	28			28
Stock Repurchased and Retired During Period, Shares			(2,334)
Stock Repurchased and Retired During Period, Value	(299)			(299)	0
Ending balance (in shares) at Sep. 30, 2018			303,670
Ending balance at Sep. 30, 2018	5,317		$ 3	134	5,199	(19)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	12
Amounts reclassified from accumulated other comprehensive income (loss)	(10)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	264				262	2
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	75			75
Stock Issued During Period, Shares, New Issues			382
Stock Issued During Period, Value, New Issues	(20)			(20)
Stock Repurchased and Retired During Period, Shares			(3,158)
Stock Repurchased and Retired During Period, Value	(292)			(189)	(103)
Ending balance (in shares) at Dec. 31, 2018			300,894
Ending balance at Dec. 31, 2018	$ 5,344		$ 3	0	5,358	(17)
Beginning balance (in shares) at Mar. 31, 2019	298,000		298,107
Beginning balance at Mar. 31, 2019	$ 5,331	[1]	$ 3	0	5,358	(30)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	1,434				1,421	13
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	73			73
Stock Issued During Period, Shares, New Issues			985
Stock Issued During Period, Value, New Issues	(48)			(48)
Stock Repurchased and Retired During Period, Shares			(3,205)
Stock Repurchased and Retired During Period, Value	(305)			(25)	(280)
Ending balance (in shares) at Jun. 30, 2019			295,887
Ending balance at Jun. 30, 2019	$ 6,485		$ 3	0	6,499	(17)
Beginning balance (in shares) at Mar. 31, 2019	298,000		298,107
Beginning balance at Mar. 31, 2019	$ 5,331	[1]	$ 3	0	5,358	(30)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	49
Amounts reclassified from accumulated other comprehensive income (loss)	(52)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 2,618
Ending balance (in shares) at Dec. 31, 2019	291,000		290,609
Ending balance at Dec. 31, 2019	$ 7,237		$ 3	0	7,267	(33)
Beginning balance (in shares) at Jun. 30, 2019			295,887
Beginning balance at Jun. 30, 2019	6,485		$ 3	0	6,499	(17)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	861				854	7
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	92			92
Stock Issued During Period, Shares, New Issues			584
Stock Issued During Period, Value, New Issues	26			26
Stock Repurchased and Retired During Period, Shares			(3,253)
Stock Repurchased and Retired During Period, Value	(306)			(118)	(188)
Ending balance (in shares) at Sep. 30, 2019			293,218
Ending balance at Sep. 30, 2019	7,158		$ 3	0	7,165	(10)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	(6)
Amounts reclassified from accumulated other comprehensive income (loss)	(17)
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	323				346	(23)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	91			91
Stock Issued During Period, Shares, New Issues			492
Stock Issued During Period, Value, New Issues	(30)			(30)
Stock Repurchased and Retired During Period, Shares			(3,101)
Stock Repurchased and Retired During Period, Value	$ (305)			(61)	(244)
Ending balance (in shares) at Dec. 31, 2019	291,000		290,609
Ending balance at Dec. 31, 2019	$ 7,237		$ 3	$ 0	$ 7,267	$ (33)

[1] Derived from audited Consolidated Financial Statements.