Significant Accounting Policies Narrative (Details) $ in Millions		6 Months Ended
	Apr. 01, 2019 USD ($)	Sep. 30, 2019 USD ($) segment	Apr. 01, 2018 USD ($)
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Number of reportable segments | segment		3
Present value of lease liabilities		$ 2,125
ROU assets		2,002
Cumulative-effect adjustment to beginning retained earnings	$ 11		$ 154
Impairment charge to ROU assets		$ 180
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment to beginning retained earnings	11		$ 154
ASU 2016-02
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Present value of lease liabilities	2,200
ROU assets	2,100
Impairment charge to ROU assets	89
ASU 2016-02 | Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cumulative-effect adjustment to beginning retained earnings	$ 69