Stock-Based Compensation And Employee Benefit Plans (Narrative) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended					12 Months Ended								3 Months Ended	12 Months Ended			12 Months Ended								1 Months Ended	12 Months Ended		17 Months Ended	1 Months Ended	12 Months Ended
	Mar. 31, 2013	Mar. 31, 2012	Mar. 31, 2011	Mar. 31, 2013 Minimum [Member]	Mar. 31, 2013 Maximum [Member]	Mar. 31, 2013 Restricted Stock Rights [Member]	Mar. 31, 2012 Restricted Stock Rights [Member]	Mar. 31, 2011 Restricted Stock Rights [Member]	Mar. 31, 2013 Employee Stock Option [Member]	Mar. 31, 2012 Employee Stock Option [Member]	Mar. 31, 2011 Employee Stock Option [Member]	Mar. 31, 2013 Performance Based Restricted Stock Units [Member]	Mar. 31, 2011 Performance Based Restricted Stock Units [Member]	Dec. 31, 2012 Market Based Restricted Stock Units [Member]	Mar. 31, 2013 Market Based Restricted Stock Units [Member]	Mar. 31, 2012 Market Based Restricted Stock Units [Member]	Mar. 31, 2013 Market Based Restricted Stock Units [Member] Target [Member]	Mar. 31, 2013 Employee Stock [Member]	Mar. 31, 2012 Employee Stock [Member]	Mar. 31, 2011 Employee Stock [Member]	Mar. 31, 2010 Employee Stock [Member]	Mar. 31, 2013 Employee Stock [Member] Minimum [Member]	Mar. 31, 2013 Employee Stock [Member] Maximum [Member]	Mar. 31, 2013 Equity Plan [Member]	Jul. 26, 2012 Equity Plan [Member]	Feb. 28, 2011 Fiscal Year 2011 Repurchase Program [Member]	Mar. 31, 2013 Fiscal Year 2011 Repurchase Program [Member]	Mar. 31, 2012 Fiscal Year 2011 Repurchase Program [Member]	Jun. 30, 2012 Fiscal Year 2011 Repurchase Program [Member]	Jul. 31, 2012 Fiscal Year 2013 Repurchase Program [Member]	Mar. 31, 2013 Fiscal Year 2013 Repurchase Program [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost related to stock-based compensation						$ 221			$ 5						$ 7
Weighted-average service period, years						1 year 8 months 12 days			2 years 1 month 17 days
Tax costs from exercise of stock options									1		2
Tax benefit from stock options exercised										3
Deferred tax write-offs									1	1	3
Excess tax benefit from stock-based compensation	0	4	1							4	1
Percentage discount that employees, officers and directors may purchase of stock lesser of market value																								100.00%
Number of years in which stock options generally expire (years)																								10 years
Percentage in which stock options become exercisable for after one year from date of grant																								24.00%
Number of months in which stock options ratably exercise after one year																								38 months
Increase in number of shares authorized																									6,180,000
Number of shares available for grant						8,300,000			11,800,000
Options Outstanding, Weighted-Average Remaining Contractual Term (in years)	4 years 6 months 15 days								4 years 6 months 15 days
Options outstanding, aggregate intrinsic value	4								4
Weighted-average grant date fair values of options granted during the period									$ 4.64	$ 7.27	$ 6.03
Intrinsic values of options exercised during the period										4	1
Share-based Compensation Arrangement by Share-based Payment Award, Options, Vested in Period, Fair Value									11	15	24
Shares used as denominator for computation of potential dilution from options outstanding	302,000,000	320,000,000
Reduction in shares available per grant of stock right						1.43
Weighted-average grant date fair value of stock-based compensation granted during period						$ 12.85	$ 21.38	$ 17.38					$ 15.39		$ 12.41	$ 33.70		$ 4.83		$ 4.98	$ 4.67
Grant date fair value of stock-based compensation vested during period						143.0	165.0	142.0				1.0			3.7
Percentage range of shares received at vesting based on total stockholder return ("TSR")				0.00%	200.00%
Target percentage of presented shares granted that may potentially vest																	100.00%
Maximum number of common shares to be earned during the performance period, Grants														1,900,000
Maximum number of common shares to be earned during the performance period, Outstanding															1,900,000
Minimum Percentage That Employees Authorized For Payroll Deductions																			2.00%
Maximum percentage that employees authorized for payroll deductions																			10.00%
Discount percent																		85.00%
Shares issued under the Employee Stock Purchase Plan during period																		3,000,000
Exercise prices for purchase rights																						$ 11.05	$ 11.33
Assets value under deferred compensation plan	11	11
Liabilities under deferred compensation plan	12	12
Contribution to 401 (k) plan and Registered Retirement Savings Plan	14	13	9
Stock Repurchase Program, Authorized Amount																										600				500
Stock Repurchase Program, Period in Force																										18 months
Repurchase and retirement of common stock, shares	26,000,000	25,000,000																									4,000,000	25,000,000	32,000,000		22,000,000
Repurchase and retirement of common stock	$ (349)	$ (471)	$ (58)																								$ 71	$ 471			$ 278