Changes in Accumulated Other Comprehensive Income by Component (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2018		Jun. 30, 2017
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	$ (127)	[1]	$ (19)
Other comprehensive income (loss) before reclassifications	63		(25)
Amounts reclassified from accumulated other comprehensive income (loss)	15		(27)
Total other comprehensive income (loss), net of tax	78		(52)
Ending balance	(26)		(71)
Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(8)		(3)
Other comprehensive income (loss) before reclassifications	0		0
Amounts reclassified from accumulated other comprehensive income (loss)	0		0
Total other comprehensive income (loss), net of tax	0		0
Ending balance	(8)		(3)
Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(89)		32
Other comprehensive income (loss) before reclassifications	78		(39)
Amounts reclassified from accumulated other comprehensive income (loss)	15		(17)
Total other comprehensive income (loss), net of tax	93		(56)
Ending balance	27		(24)
Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Beginning balance	(30)		(48)
Other comprehensive income (loss) before reclassifications	(15)		14
Amounts reclassified from accumulated other comprehensive income (loss)	0		(10)
Total other comprehensive income (loss), net of tax	(15)		4
Ending balance	(45)		$ (44)
ASU 2018-02 [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Amounts reclassified from accumulated other comprehensive income (loss)	1
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Other comprehensive income (loss) before reclassifications	22
Ending balance	7
Adjustments for New Accounting Pronouncement on April 1, 2018 [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Ending balance	(104)
Adjustments for New Accounting Pronouncement on April 1, 2018 [Member] | Unrealized Gains (Losses) on Available-for-Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Ending balance	(8)
Adjustments for New Accounting Pronouncement on April 1, 2018 [Member] | Unrealized Gains (Losses) on Derivative Instruments [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Ending balance	(66)
Adjustments for New Accounting Pronouncement on April 1, 2018 [Member] | Foreign Currency Translation Adjustment [Member]
Accumulated Other Comprehensive Income (Loss) [Roll Forward]
Ending balance	$ (30)

[1] Derived from audited Consolidated Financial Statements.