Retirement-Related Benefits (Details 3) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Retirement-Related Benefits:
Defined benefit and contribution pension plans - cost	$ 749us-gaap_PensionExpense	$ 474us-gaap_PensionExpense
Nonpension postretirement plans - cost	71	67
Total	$ 820	$ 541
Year-to-year percent change, defined benefit and contribution pension plans cost	58.00%ibm_PensionExpenseChangePercent
Year-to-year percent change, Nonpension postretirement plans cost	6.20%
Year-to-year percent change, total	51.60%

The amount of pension and other (such as medical, dental and life insurance) postretirement benefit costs recognized during the period for (1) defined benefit plans (periodic benefit costs include the following components: service cost, interest cost, expected return on plan assets, gain (loss) on assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments) and for (2) defined contribution plans (to the extent that a plan's defined contributions to an individual's account are to be made for periods in which that individual renders services, the net cost for a period is the contribution called for in that period; if a plan calls for contributions for periods after an individual retires or terminates, the estimated cost is accrued during the employee's service period).

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The amount of pension benefit costs recognized during the period for (1) defined benefit plans and (2) defined contribution plans. For defined benefit plans, pension expense includes the following components: service cost, interest cost, expected return on plan assets, gain (loss) on plan assets, prior service cost or credit, transition asset or obligation, and gain (loss) due to settlements or curtailments. For defined contribution plans, the pension expense generally equals the firm's contribution to employees' accounts (if the firm contributes) during the period.

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