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Defined Benefits (Details) - USD ($)
$ in Millions
3 Months Ended
Mar. 31, 2016
Mar. 31, 2015
Defined Benefit Plan    
Defined Benefit Plan Disclosure [Line Items]    
Service cost $ 10 $ 1
Interest cost 19 2
Expected return on plan assets (23) (3)
Amortization of:    
Actuarial (gain) loss 5 1
Net periodic defined benefit costs (credits) $ 11 1
Talen Energy Supply | Supplemental Retirement Plan    
Net Periodic Defined Benefit Costs Allocated to Subsidiary by Sponsor (Numeric) [Abstract]    
Costs allocated to subsidiary by plan sponsors   $ 11