Financing Arrangement (Tables)
 6 Months Ended
Sep. 30, 2016
Debt Instruments [Abstract]  
Carrying Values Of Liability And Equity Components Of Notes
The carrying and fair values of the Convertible Notes are as follows (in millions): 
  
As of
September 30, 2016
 
As of
March 31, 2016
Principal amount of Convertible Notes
$
—

 
$
163

Unamortized debt discount of the liability component
—

 
(2
)
Net carrying value of Convertible Notes
$
—

 
$
161

 
 
 
 
Fair value of Convertible Notes (Level 2)
$
—

 
$
338
Schedule of Carrying Values Of Liability and Equity Components of Senior Notes [Table Text Block]
The carrying and fair values of the Senior Notes are as follows (in millions): 
  
As of
September 30, 2016
 
As of
March 31, 2016
Senior Notes:
 
 
 
3.70% Senior Notes due 2021
$
600

 
$
600

4.80% Senior Notes due 2026
400

 
400

Total principal amount
$
1,000

 
$
1,000

Unaccreted discount
(2
)
 
(2
)
Unamortized debt issuance costs
(8
)
 
(9
)
Net carrying value of Senior Notes
$
990

 
$
989

 
 
 
 
Fair value of Senior Notes (Level 2)
$
1,082

 
$
1,039
Schedule Of Interest Expense
The following table summarizes our interest expense recognized for the three and six months ended September 30, 2016 and 2015 that is included in interest and other income (expense), net on our Condensed Consolidated Statements of Operations (in millions): 
 
Three Months Ended
September 30,
 
Six Months Ended
September 30,
 
2016
 
2015
 
2016
 
2015
Amortization of debt discount
(1
)
 
(5
)
 
(2
)
 
(11
)
Amortization of debt issuance costs
—

 
—

 
(1
)
 
(1
)
Coupon interest expense
(10
)
 
(1
)
 
(21
)
 
(2
)
Total interest expense
$
(11
)
 
$
(6
)
 
$
(24
)
 
$
(14
)