Intangible Assets Including Goodwill (Details 2) (USD $) In Millions	9 Months Ended
Sep. 30, 2011
Future amortization expense, by year
2011 (for Q4)	$ 288
2012	981
2013	710
2014	415
2015	265
Capitalized software
Future amortization expense, by year
2011 (for Q4)	145
2012	424
2013	194
2014	42
Acquired intangibles
Future amortization expense, by year
2011 (for Q4)	143
2012	557
2013	515
2014	374
2015	$ 265

The amount of amortization expense expected to be recognized during the first full fiscal year following the date of the most recent balance sheet.

Name:	ibm_FutureAmortizationExpenseFirstFullFiscalYear
Namespace Prefix:	ibm
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of amortization expense expected to be recognized during the fourth full fiscal year following the date of the most recent balance sheet.

Name:	ibm_FutureAmortizationExpenseFourthFullFiscalYear
Namespace Prefix:	ibm
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of amortization expense expected to be recognized during the second full fiscal year following the date of the most recent balance sheet.

Name:	ibm_FutureAmortizationExpenseSecondFullFiscalYear
Namespace Prefix:	ibm
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

The amount of amortization expense expected to be recognized during the third full fiscal year following the date of the most recent balance sheet.

Name:	ibm_FutureAmortizationExpenseThirdFullFiscalYear
Namespace Prefix:	ibm
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

Name:	us-gaap_FiniteLivedIntangibleAssetsFutureAmortizationExpenseAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

The amount of amortization expense expected to be recognized during the remainder of the current fiscal year.

Name:	us-gaap_FutureAmortizationExpenseRemainderOfFiscalYear
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration