Stock-Based Compensation and Earnings Per Share (Stock Option Fair Value Information) (Details) - USD ($) shares in Millions, $ in Millions |
6 Months Ended | 12 Months Ended | |
|---|---|---|---|
Mar. 31, 2016 |
Mar. 31, 2015 |
Sep. 30, 2015 |
|
| Options Assumptions [Line Items] | |||
| Risk Free Interest Rate, Minimum | 0.80% | 0.50% | |
| Risk Free Interest Rate, Maximum | 2.50% | 2.60% | |
| Expected dividend yield | 1.60% | ||
| Expected volatility | 20.00% | 24.00% | |
| Expected life | 7 years | 7 years | |
| Company Common Stock Shares Issued To Employees Under Employee Stock Purchase And Defined Contribution Savings Plans | 0.3 | 0.3 | |
| Compensation and benefits paid in common stock | $ 27 | $ 23 | |
| Minimum [Member] | |||
| Options Assumptions [Line Items] | |||
| Expected dividend yield | 1.50% | ||
| Maximum [Member] | |||
| Options Assumptions [Line Items] | |||
| Expected dividend yield | 1.60% | ||