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, 2019			298,107
Beginning balance at Mar. 31, 2019	$ 5,331		$ 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			298,107
Beginning balance at Mar. 31, 2019	5,331		$ 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			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			290,609
Ending balance at Dec. 31, 2019	$ 7,237		$ 3	0	7,267	(33)
Beginning balance (in shares) at Mar. 31, 2020	288,000		288,413
Beginning balance at Mar. 31, 2020	$ 7,461	[1]	$ 3	0	7,508	(50)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	363				365	(2)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	102			102
Stock Issued During Period, Shares, New Issues			1,088
Stock Issued During Period, Value, New Issues	(66)			(66)
Stock Repurchased and Retired During Period, Shares			(747)
Stock Repurchased and Retired During Period, Value	(78)			(36)	(42)
Ending balance (in shares) at Jun. 30, 2020			288,754
Ending balance at Jun. 30, 2020	$ 7,782		$ 3	0	7,831	(52)
Beginning balance (in shares) at Mar. 31, 2020	288,000		288,413
Beginning balance at Mar. 31, 2020	$ 7,461	[1]	$ 3	0	7,508	(50)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	(58)
Amounts reclassified from accumulated other comprehensive income (loss)	14
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	$ 717
Ending balance (in shares) at Dec. 31, 2020	288,000		288,443
Ending balance at Dec. 31, 2020	$ 7,963		$ 3	0	8,054	(94)
Beginning balance (in shares) at Jun. 30, 2020			288,754
Beginning balance at Jun. 30, 2020	7,782		$ 3	0	7,831	(52)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	148				185	(37)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	113			113
Stock Issued During Period, Shares, New Issues			868
Stock Issued During Period, Value, New Issues	32			32
Stock Repurchased and Retired During Period, Shares			0
Stock Repurchased and Retired During Period, Value	0			0	0
Ending balance (in shares) at Sep. 30, 2020			289,622
Ending balance at Sep. 30, 2020	8,075		$ 3	145	8,016	(89)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Other comprehensive income (loss) before reclassifications	(25)
Amounts reclassified from accumulated other comprehensive income (loss)	20
Comprehensive Income (Loss), Net of Tax, Attributable to Parent	206				211	(5)
APIC, Share-based Payment Arrangement, Increase for Cost Recognition	111			111
Stock Issued During Period, Shares, New Issues			1,345
Stock Issued During Period, Value, New Issues	(54)			(54)
Stock Repurchased and Retired During Period, Shares			(2,524)
Stock Repurchased and Retired During Period, Value	(326)			(202)	(124)
Cash dividends declared ($0.17 per common share)	$ (49)				(49)
Common Stock, Dividends, Per Share, Declared	$ 0.17
Ending balance (in shares) at Dec. 31, 2020	288,000		288,443
Ending balance at Dec. 31, 2020	$ 7,963		$ 3	$ 0	$ 8,054	$ (94)

[1] Derived from audited Consolidated Financial Statements.