Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017		Dec. 31, 2016
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (73)	$ (10)	$ (19)	[1]	$ (16)
Other comprehensive income (loss) before reclassifications	(30)	17	(52)		34
Amounts reclassified from accumulated other comprehensive income (loss)	8	(8)	(24)		(19)
Total other comprehensive income (loss), net of tax	(22)	9	(76)		15
Ending balance	(95)	(1)	(95)		(1)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(3)	1	(3)		1
Other comprehensive income (loss) before reclassifications	(4)	(5)	(4)		(4)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	0		(1)
Total other comprehensive income (loss), net of tax	(4)	(5)	(4)		(5)
Ending balance	(7)	(4)	(7)		(4)
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(58)	31	32		14
Other comprehensive income (loss) before reclassifications	(14)	39	(82)		66
Amounts reclassified from accumulated other comprehensive income (loss)	8	(8)	(14)		(18)
Total other comprehensive income (loss), net of tax	(6)	31	(96)		48
Ending balance	(64)	62	(64)		62
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(12)	(42)	(48)		(31)
Other comprehensive income (loss) before reclassifications	(12)	(17)	34		(28)
Amounts reclassified from accumulated other comprehensive income (loss)	0	0	(10)		0
Total other comprehensive income (loss), net of tax	(12)	(17)	24		(28)
Ending balance	$ (24)	$ (59)	$ (24)		$ (59)

[1] Derived from audited Consolidated Financial Statements.