Stockholders' Equity - Changes in Stockholders Equity (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Changes in Stockholders' Equity
Beginning balance	$ 114,803	$ 73,728	$ 93,404	$ 62,060	$ 82,775
Other comprehensive income (loss)	(550)	426	(895)	(43)
Net Income	3,156	6,331	19,041	14,109	26,263	$ 17,377
Ending balance	120,564	82,775	120,564	82,775	120,564	82,775
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	48,724	38,017	42,865	33,658	40,307
Stock-based compensation and issuance of employee benefit plan stock	3,155	2,290	9,014	6,649
Ending balance	51,879	40,307	51,879	40,307	51,879	40,307
Accumulated other comprehensive income (loss)
Changes in Stockholders' Equity
Beginning balance	(525)	(1,455)	(180)	(986)	(1,029)
Other comprehensive income (loss)	(550)	426	(895)	(43)
Ending balance	(1,075)	(1,029)	(1,075)	(1,029)	(1,075)	(1,029)
Retained earnings
Changes in Stockholders' Equity
Beginning balance	68,436	38,998	52,551	31,220	45,329
Net Income	3,156	6,331	19,041	14,109
Ending balance	$ 71,592	$ 45,329	$ 71,592	$ 45,329	$ 71,592	$ 45,329