Stockholders' Equity - Changes in Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Changes in Stockholders' Equity
Beginning balance	$ 73,728	$ 53,061	$ 62,060	$ 43,549	$ 56,508
Other comprehensive income (loss)	426	(469)	(43)	(394)
Net Income	6,331	2,134	14,109	8,320	17,377	$ 11,347
Ending balance	82,775	56,508	82,775	56,508	82,775	56,508
Common stock
Changes in Stockholders' Equity
Beginning balance	5	5	5	5	5
Ending balance	5	5	5	5	5	5
Treasury stock
Changes in Stockholders' Equity
Beginning balance	(1,837)	(1,837)	(1,837)	(1,837)	(1,837)
Ending balance	(1,837)	(1,837)	(1,837)	(1,837)	(1,837)	(1,837)
Additional paid-in capital
Changes in Stockholders' Equity
Beginning balance	38,017	30,035	33,658	26,791	31,817
Stock-based compensation and issuance of employee benefit plan stock	2,290	1,782	6,649	5,026
Ending balance	40,307	31,817	40,307	31,817	40,307	31,817
Accumulated other comprehensive income (loss)
Changes in Stockholders' Equity
Beginning balance	(1,455)	(960)	(986)	(1,035)	(1,429)
Other comprehensive income (loss)	426	(469)	(43)	(394)
Ending balance	(1,029)	(1,429)	(1,029)	(1,429)	(1,029)	(1,429)
Retained earnings
Changes in Stockholders' Equity
Beginning balance	38,998	25,818	31,220	19,625	27,952
Net Income	6,331	2,134	14,109	8,320
Ending balance	$ 45,329	$ 27,952	$ 45,329	27,952	$ 45,329	$ 27,952
Retained earnings | Cumulative Effect, Period of Adoption, Adjustment
Changes in Stockholders' Equity
Beginning balance				$ 7