14. Trade accounts receivable

As of December 31, trade accounts receivable were as follows:

€ in millions	2011	2010
Trade accounts receivable	3,617	3,252
less allowance for doubtful accounts	383	317
Trade accounts receivable, net	3,234	2,935

All trade accounts receivable are due within one year.

The following table shows the development of the allowance for doubtful accounts during the fiscal year:

€ in millions	2011	2010
Allowance for doubtful accounts at the beginning of the year	317	285
Change in valuation allowances as recorded in the consolidated statement of income	216	175
Write-offs and recoveries of amounts previously written-off	-154	-158
Foreign currency translation	4	15
Allowance for doubtful accounts at the end of the year	383	317

The following table shows the ageing analysis of trade accounts receivable and their allowance for doubtful accounts:

€ in millions	not overdue	up to 3 months overdue	3 to 6 months overdue	6 to 12 months overdue	more than 12 months overdue	Total
Trade accounts receivable	1,965	606	295	306	445	3,617
less allowance for doubtful accounts	22	49	43	64	205	383
Trade accounts receivable, net	1,943	557	252	242	240	3,234