Income Taxes (Narrative) (Details) - USD ($)
$ in Millions |
3 Months Ended |
6 Months Ended |
Sep. 30, 2016 |
Sep. 30, 2015 |
Sep. 30, 2016 |
Sep. 30, 2015 |
| Income Tax Footnote Disclosure [Line Items] |
|
|
|
|
| Effective tax rates |
26.90%
|
9.40%
|
19.60%
|
20.70%
|
| United States statutory tax rate |
35.00%
|
35.00%
|
35.00%
|
35.00%
|
| Excess Tax Benefit from Share-based Compensation, Financing Activities |
$ 4
|
$ 25
|
$ 37
|
$ 65
|
| Unrecognized tax benefits, period increase (decrease) |
10
|
|
18
|
|
| Gross unrecognized tax benefits |
349
|
|
349
|
|
| Amount of unrecognized tax benefits that would affect the effective tax rate |
322
|
|
322
|
|
| The total amount of unrecognized tax benefits that, if recognized, would result in adjustments to deferred tax assets with corresponding adjustments to the valuation allowance |
|
|
28
|
|
| Unrecognized tax benefits income tax penalties and interest accrued increase (decrease) |
1
|
|
2
|
|
| Combined amount of accrued interest and penalties related to uncertain tax positions |
16
|
|
16
|
|
| Maximum |
|
|
|
|
| Income Tax Footnote Disclosure [Line Items] |
|
|
|
|
| Amount of unrecognized tax benefits for which it is reasonably possible that there will be a reduction within the next 12 months |
$ 67
|
|
$ 67
|
|