Stockholders' Equity (Narrative) (Details) - USD ($) shares in Millions, $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Jul. 30, 2020
Stockholders Equity Note [Line Items]
Repurchases of capital stock	$ 6,852	$ 3,577	$ 15,348	$ 6,602
Class C Capital Stock | Share Repurchase Program
Stockholders Equity Note [Line Items]
Authorized share repurchase amount	25,000		25,000
Remaining amount available for repurchase	$ 5,400		$ 5,400
Repurchases of capital stock (in shares)			11.6
Repurchases of capital stock			$ 15,300
Class C Capital Stock | Share Repurchase Program | Subsequent Event
Stockholders Equity Note [Line Items]
Authorized share repurchase amount					$ 28,000