Condensed Consolidated Statement of Comprehensive Income (Unaudited) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Statement of Comprehensive Income [Abstract]
Net income	$ 3,292	$ 2,224
Currency translation adjustments, net of deferred taxes of $(92) and $(7)	(35)	(2,157)
Cash flow hedges:
Deferred gains (losses), net of deferred taxes of $(19) and $10	119	54
Realized (gains) losses reclassified to net income, net of deferred taxes of $— and $17	0	(106)
Employee benefit obligations and other, net of deferred taxes of $2 and $3	(10)	(7)
Comprehensive income	3,366	8
Less: Net income (loss) attributable to noncontrolling interests and redeemable subsidiary preferred stock	(37)	77
Less: Other comprehensive income (loss) attributable to noncontrolling interests	(14)	(25)
Comprehensive income (loss) attributable to Comcast Corporation	$ 3,417	$ (44)