Stockholders' Equity - Changes in Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019	Jul. 01, 2019	Dec. 31, 2018	Jul. 01, 2018
Stockholders' equity	$ 65,272	$ 48,410	$ 65,272	$ 48,410	$ 62,060		$ 43,549
Other comprehensive income (loss)	(1,077)	25
Net Income	2,535	3,561	10,563	12,005
Common stock
Stockholders' equity	5	5	5	5	5		5
Treasury stock
Stockholders' equity	(1,837)	(1,837)	(1,837)	(1,837)	(1,837)		(1,837)
Additional paid-in capital
Stockholders' equity	35,412	28,059	35,412	28,059	33,658		26,791
Stock-based compensation and issuance of employee benefit plan stock	1,754	1,268
Accumulated other comprehensive income (loss)
Stockholders' equity	(2,063)	(1,010)	(2,063)	(1,010)	(986)		(1,035)
Other comprehensive income (loss)	(1,077)	25
Retained earnings
Stockholders' equity	33,755	23,193	$ 33,755	$ 23,193	$ 31,220		$ 19,625
Cumulative effect of changes in accounting principles						$ 0		$ 7
Net Income	$ 2,535	$ 3,561