Taxes (Details 3) $ in Millions	Dec. 31, 2015 USD ($)
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	$ 10,000
State Jurisdiction
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	7,176
State Jurisdiction | 2016-2020
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	403
State Jurisdiction | 2021-2025
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	1,323
State Jurisdiction | 2023-2030
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	2,205
State Jurisdiction | 2031-2035
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	3,245
Local Jurisdiction
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	2,983
Local Jurisdiction | 2016-2020
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	2,983
Local Jurisdiction | 2021-2025
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	0
Local Jurisdiction | 2023-2030
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	0
Local Jurisdiction | 2031-2035
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	0
FES | State Jurisdiction
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	1,550
FES | State Jurisdiction | 2016-2020
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	95
FES | State Jurisdiction | 2021-2025
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	68
FES | State Jurisdiction | 2023-2030
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	259
FES | State Jurisdiction | 2031-2035
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	1,128
FES | Local Jurisdiction
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	1,820
FES | Local Jurisdiction | 2016-2020
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	1,820
FES | Local Jurisdiction | 2021-2025
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	0
FES | Local Jurisdiction | 2023-2030
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	0
FES | Local Jurisdiction | 2031-2035
Pre-tax net operating loss expiration period
Pre-tax net operating loss carryforwards for state and local income tax purposes	$ 0