Income Taxes - Additional Information (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Mar. 31, 2017
Income Tax Disclosure [Line Items]
Provision for income tax expense (benefit)	$ (2,821)	$ (29)	$ (2,655)	$ 212
Income tax benefit attributable to revaluation of net deferred tax liabilities due to reduction of federal statutory income tax rate			$ (2,900)
Federal statutory income tax rate			35.00%
Estimated federal statutory income tax blended rate			31.55%
Deferred tax assets	1,800		$ 1,800		$ 1,000
Net deferred income tax liability	$ 5,400		$ 5,400		$ 7,900
Tax Year 2018 [Member]
Income Tax Disclosure [Line Items]
Federal statutory income tax rate			21.00%