Condensed Consolidating Financial Information (Condensed Consolidating Statement of Cash Flows) (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Operating Activities
Net cash provided by (used in) operating activities	$ 4,393	$ 3,468
Investing Activities
Net transactions with affiliates	0	0
Capital expenditures	(1,174)	(1,106)
Cash paid for intangible assets	(184)	(123)
Acquisitions, net of cash acquired	0	(5,658)
Proceeds from sales of businesses and investments	35	18
Purchases of investments	(62)	(16)
Other	36	(2)
Net cash provided by (used in) investing activities	(1,349)	(6,887)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	(407)	1,677
Repurchases and repayments of debt	(1,125)	(1,759)
Repurchases and retirements of common stock	(750)	(525)
Dividends paid	(304)	(261)
Issuances of common stock	150	129
Distributions (to) from noncontrolling interests	(58)	(46)
Other	37	42
Net cash provided by (used in) financing activities	(2,457)	(743)
Increase (decrease) in cash and cash equivalents	587	(4,162)
Cash and cash equivalents, beginning of period	1,620	5,984
Cash and cash equivalents, end of period	2,207	1,822
Comcast [Member]
Operating Activities
Net cash provided by (used in) operating activities	(242)	(210)
Investing Activities
Net transactions with affiliates	1,639	(102)
Capital expenditures	(2)	(2)
Cash paid for intangible assets	(1)	0
Acquisitions, net of cash acquired		0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	1,636	(104)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	1,688
Proceeds from borrowings	0	0
Repurchases and repayments of debt	(563)	(750)
Repurchases and retirements of common stock	(750)	(525)
Dividends paid	(304)	(261)
Issuances of common stock	150	129
Distributions (to) from noncontrolling interests	0	0
Other	73	33
Net cash provided by (used in) financing activities	(1,394)	314
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
CCCL Parent [Member]
Operating Activities
Net cash provided by (used in) operating activities	53	24
Investing Activities
Net transactions with affiliates	(53)	976
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions, net of cash acquired		0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	(53)	976
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	(1,000)
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions (to) from noncontrolling interests	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	(1,000)
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Combined CCHMO Parents [Member]
Operating Activities
Net cash provided by (used in) operating activities	(77)	(75)
Investing Activities
Net transactions with affiliates	630	75
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions, net of cash acquired		0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	630	75
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	(553)	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions (to) from noncontrolling interests	0	0
Other	0	0
Net cash provided by (used in) financing activities	(553)	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Comcast Holdings [Member]
Operating Activities
Net cash provided by (used in) operating activities	(9)	(15)
Investing Activities
Net transactions with affiliates	9	15
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions, net of cash acquired		0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	9	15
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions (to) from noncontrolling interests	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	0	0
Comcast Non-Guarantor Subsidiaries [Member]
Operating Activities
Net cash provided by (used in) operating activities	4,668	3,744
Investing Activities
Net transactions with affiliates	(2,225)	(964)
Capital expenditures	(1,172)	(1,104)
Cash paid for intangible assets	(183)	(123)
Acquisitions, net of cash acquired		(5,658)
Proceeds from sales of businesses and investments	35	18
Purchases of investments	(62)	(16)
Other	36	(2)
Net cash provided by (used in) investing activities	(3,571)	(7,849)
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	(407)	(11)
Proceeds from borrowings	0	0
Repurchases and repayments of debt	(9)	(9)
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions (to) from noncontrolling interests	(58)	(46)
Other	(36)	9
Net cash provided by (used in) financing activities	(510)	(57)
Increase (decrease) in cash and cash equivalents	587	(4,162)
Cash and cash equivalents, beginning of period	1,620	5,984
Cash and cash equivalents, end of period	2,207	1,822
Elimination and Consolidation Adjustments [Member]
Operating Activities
Net cash provided by (used in) operating activities	0	0
Investing Activities
Net transactions with affiliates	0	0
Capital expenditures	0	0
Cash paid for intangible assets	0	0
Acquisitions, net of cash acquired		0
Proceeds from sales of businesses and investments	0	0
Purchases of investments	0	0
Other	0	0
Net cash provided by (used in) investing activities	0	0
Financing Activities
Proceeds from (repayments of) short-term borrowings, net	0	0
Proceeds from borrowings	0	0
Repurchases and repayments of debt	0	0
Repurchases and retirements of common stock	0	0
Dividends paid	0	0
Issuances of common stock	0	0
Distributions (to) from noncontrolling interests	0	0
Other	0	0
Net cash provided by (used in) financing activities	0	0
Increase (decrease) in cash and cash equivalents	0	0
Cash and cash equivalents, beginning of period	0	0
Cash and cash equivalents, end of period	$ 0	$ 0