Interim Financial Data - Cumulative Effect of Changes in Consolidated Balance Sheet for Adoption of Revenue Recognition (Details) - USD ($) $ in Millions	Sep. 30, 2018	Apr. 01, 2018	Mar. 31, 2018
ASSETS
Other assets	$ 1,515		$ 1,614
LIABILITIES AND SHAREHOLDER’S EQUITY
Deferred income taxes	5,373		5,326
Other liabilities	4,405		3,987
Retained earnings	12,156		$ 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	(74)	73
LIABILITIES AND SHAREHOLDER’S EQUITY
Deferred income taxes	37	(36)
Other liabilities	(224)	219
Retained earnings	$ 113	$ (110)