Britney Spears still earns almost $750,000 (£375,000) each month - even though she hasn't released any music in two years.The singer's earnings have been revealed in court documents, linked to Spears' battle with her ex-husband Kevin Federline over custody of their two children, Sean Preston, 23 months and Jayden James, 11 months.The documents, obtained by Tmz.com, reveal Spears' average monthly salary is $737,868 (£369,434). They also reveal she pays $20,000 (£10,000) a month in spousal support to Federline, payments that cease in November (07).Federline's lawyers are using the revelations to claim that Spears "is clearly the 'monied party' in this case" and should pay $50,000 (£25,000) for custody hearing expenses.Spears hasn't released an album since B in the Mix: The Remixes in 2005. Her last LP containing new material was Into The Zone in 2003.