Expense Example (Core Bond Trust, USD $)	12 Months Ended
	May 01, 2011
Series I, Core Bond Trust
Expense Example:
Year 1	$ 70
Year 3	221
Year 5	384
Year 10	859
Series II, Core Bond Trust
Expense Example:
Year 1	91
Year 3	284
Year 5	493
Year 10	1,096
Series NAV, Core Bond Trust
Expense Example:
Year 1	65
Year 3	205
Year 5	357
Year 10	$ 798