Benefit Plans - Assets of Benefit Plans (Details) (USD $) In Millions	6 Months Ended
Jun. 30, 2011
Assets of benefit plans [Line Items]
Employer contributions made directly to pension plan assets	$ 229

Name:

pgn_EmployerContributionsDirectlyToPensionPlanAssets

Namespace Prefix:

pgn

Data Type:

xbrli:monetaryItemType

Balance Type:

debit

Period Type:

duration