14. Trade accounts receivable

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

€ in millions	2010	2009
Trade accounts receivable	3,252	2,794
less allowance for doubtful accounts	317	285
Trade accounts receivable, net	2,935	2,509

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	2010	2009
Allowance for doubtful accounts at the beginning of the year	285	257
Change in valuation allowances as recorded in the consolidated statement of income	175	174
Write-offs and recoveries of amounts previously written-off	-158	-141
Foreign currency translation	15	-5
Allowance for doubtful accounts at the end of the year	317	285

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	1,894	527	254	237	340	3,252
less allowance for doubtful accounts	16	43	33	53	172	317
Trade accounts receivable, net	1,878	484	221	184	168	2,935