Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016
Income Tax Footnote Disclosure [Line Items]
Effective tax rates	14.00%	20.30%
United States statutory tax rate	35.00%
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	$ 55
Increase to net cash provided by Operating Activities [Member]
Income Tax Footnote Disclosure [Line Items]
Excess Tax Benefit from Share-based Compensation, Operating Activities		$ 33
Excluding excess tax benefit [Member]
Income Tax Footnote Disclosure [Line Items]
Effective tax rates	19.20%
Provision for income taxes [Member] | Increase to net cash provided by Operating Activities [Member]
Income Tax Footnote Disclosure [Line Items]
Excess Tax Benefit from Share-based Compensation, Operating Activities	$ 39