Accounting for Share-Based Compensation 2 (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Jun. 30, 2012
Unrecognized share based compensation cost
Unrecognized Compensation Costs	$ 166
Weighted Average Period Expected to be Recognized	2 years 6 months
Stock Option Awards [Member]
Unrecognized share based compensation cost
Unrecognized Compensation Costs	8
Weighted Average Period Expected to be Recognized	2 years 6 months
Restricted Stock Units [Member]
Unrecognized share based compensation cost
Unrecognized Compensation Costs	22
Weighted Average Period Expected to be Recognized	2 years 3 months 18 days
Restricted Stock Awards [Member]
Unrecognized share based compensation cost
Unrecognized Compensation Costs	94
Weighted Average Period Expected to be Recognized	2 years 3 months 18 days
Performance Share Units [Member]
Unrecognized share based compensation cost
Unrecognized Compensation Costs	$ 42
Weighted Average Period Expected to be Recognized	3 years