v2.4.0.8

Long-Term Debt (Narrative) (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Total debt	$ 46,500,000,000
Long-term Debt, Fair Value	52,600,000,000
Amounts available under revolving credit facilities	6,300,000,000
Repurchases and repayments of debt	3,163,000,000	2,195,000,000
Comcast ownership in cable holding company subsidiaries	100.00%
Proceeds from (repayments of) short-term borrowings, net	(343,000,000)	348,000,000
NBCUniversal Media, LLC [Member]
Total debt	10,300,000,000
Long-term Debt, Fair Value	11,400,000,000
Comcast ownership in cable holding company subsidiaries	100.00%
Related Party Aggregate Principal Amount Senior Notes Not Subject To Guarantee	4,000,000,000
Related Party Credit Facility Not Subject To Guarantee	1,350,000,000
Related Party Liquidation Preference Preferred Stock Not Subject To Guarantee	725,000,000
NBCUniversal Enterprise Credit Facility
Debt Instrument, Maturity Date, Description	March 2018
Credit facility borrowing capacity	1,350,000,000
Amounts available under revolving credit facilities	340,000,000
Repurchases and repayments of debt	1,250,000,000
NBCUniversal Enterprise Commercial Paper [Member]
Credit facility borrowing capacity	1,350,000,000
Commercial paper	1,000,000,000
Proceeds from (repayments of) short-term borrowings, net	990,000,000
Comcast And Comcast Cable Revolving Credit Facility [Member] | NBCUniversal Media, LLC [Member]
Debt Instrument, Maturity Date, Description	2017
Guarantee Obligations Revolving Credit Facility	6,250,000,000
Comcast And Comcast Cable Debt Securities [Member] | NBCUniversal Media, LLC [Member]
Guarantee Obligations Current Principal Balance	30,700,000,000
Senior 3.60% Notes Due 2024 [Member]
Principal amount	1,200,000,000
Interest rate	3.60%
Debt Instrument, Maturity Date, Description	2024
Senior 4.75% Notes Due 2044 [Member]
Principal amount	1,000,000,000
Interest rate	4.75%
Debt Instrument, Maturity Date, Description	2044
Senior 5.3% Notes Due 2014 [Member]
Interest rate	5.30%
Debt Instrument, Maturity Date, Description	2014
Repurchases and repayments of debt	1,000,000,000
Senior 2.1% Notes Due 2014 [Member]
Interest rate	2.10%
Debt Instrument, Maturity Date, Description	April 2014
Repurchases and repayments of debt	900,000,000
Senior 2.1% Notes Due 2014 [Member] | NBCUniversal Media, LLC [Member]
Interest rate	2.10%
Debt Instrument, Maturity Date, Description	April 2014
Repurchases and repayments of debt	$ 900,000,000

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Carrying value as of the balance sheet date of short-term borrowings using unsecured obligations issued by banks, corporations and other borrowers to investors. The maturities of these money market securities generally do not exceed 270 days.

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