Basis of Presentation and Significant Accounting Policies - Impact on Consolidated Balance Sheet for Adoption of ASU-2014-09 (Details) - USD ($) $ in Millions	Mar. 31, 2019	Apr. 01, 2018	Mar. 31, 2018
ASSETS
Other assets	$ 1,981		$ 1,614
LIABILITIES AND SHAREHOLDER’S EQUITY
Deferred income taxes	5,452		5,326
Other liabilities	4,564		3,987
Retained earnings	12,658		$ 11,992
Accounting Standards Update 2014-09 [Member]
ASSETS
Other assets		$ 1,687
LIABILITIES AND SHAREHOLDER’S EQUITY
Deferred income taxes		5,290
Other liabilities		4,206
Retained earnings		11,882
Adjustments Related to Adoption [Member] | Accounting Standards Update 2014-09 [Member]
ASSETS
Other assets	(72)	73
LIABILITIES AND SHAREHOLDER’S EQUITY
Deferred income taxes	38	(36)
Other liabilities	(225)	219
Retained earnings	115	$ (110)
Balances without Adoption [Member] | Accounting Standards Update 2014-09 [Member]
ASSETS
Other assets	1,909
LIABILITIES AND SHAREHOLDER’S EQUITY
Deferred income taxes	5,490
Other liabilities	4,339
Retained earnings	$ 12,773