Stockholders' Equity - Changes in Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended		12 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Mar. 31, 2019	Mar. 31, 2018	Jan. 01, 2019	Dec. 31, 2018	Jan. 01, 2018	Dec. 31, 2017
Stockholders' equity	$ 48,410	$ 31,463	$ 48,410	$ 31,463		$ 43,549		$ 27,709
Other comprehensive income (loss)	25	17
Net Income	3,561	1,629	12,005	3,938
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	28,059	22,563	28,059	22,563		26,791		21,389
Stock-based compensation and issuance of employee benefit plan stock	1,268	1,174
Accumulated other comprehensive income (loss)
Stockholders' equity	(1,010)	(467)	(1,010)	(467)		(1,035)		(484)
Other comprehensive income (loss)	25	17
Retained earnings
Stockholders' equity	23,193	11,199	$ 23,193	$ 11,199		$ 19,625		$ 8,636
Cumulative effect of changes in accounting principles					$ 7		$ 934
Net Income	$ 3,561	$ 1,629