Income Taxes (Narrative) (Details) - USD ($) $ in Millions	3 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Mar. 31, 2017
Income Tax Disclosure [Abstract]
Income Tax Reconciliation, Change in Deferred Tax Assets Valuation Allowance	$ 33	$ 142
Income tax benefit	292	56
Increase deferred tax liability for business activity changes	65	0
Unrecognized tax benefit	195		$ 190
Income Taxes Paid, Net	$ 32	$ 21