Description Of Business And Basis of Presentation New revenue standard adoption (Narrative) (Details) - USD ($) $ in Millions		3 Months Ended												12 Months Ended
	Apr. 01, 2018	Mar. 31, 2019		Dec. 31, 2018	[1]	Sep. 30, 2018	[1]	Jun. 30, 2018	[1]	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2019		Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net revenue		$ 1,238	[1]	$ 1,289		$ 1,286		$ 1,137		$ 1,582	$ 1,160	$ 959	$ 1,449	$ 4,950	[1]	$ 5,150	$ 4,845
Retained Earnings (Accumulated Deficit)		$ 5,358								$ 4,062				5,358		4,062
Service and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net revenue														3,357		$ 2,564	$ 2,205
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Sales return and price protection reserves	$ 158
Retained Earnings (Accumulated Deficit)	590
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Service and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net revenue														530
Cost of Sales [Member] | Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Mobile platform fees	$ 64													$ 188
Transferred at Point in Time [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Information Used to Allocate Transaction Price														0.75
Transferred over Time [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenue, Information Used to Allocate Transaction Price														0.25
Difference between Revenue Guidance in Effect before and after Topic 606 [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Increase (Decrease) in Deferred Revenue														$ 740
Net revenue														107
Difference between Revenue Guidance in Effect before and after Topic 606 [Member] | Service and other [Member]
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Net revenue														$ 718

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