Supplemental Compensation Plans, Directors Retirement Plan (Details) $ in Millions	12 Months Ended
	Dec. 31, 2015 USD ($)
Salary Continuation Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Duration for benefit payment after retirement age	10 years
Retirement age	65 years
Reduced benefit age	55 years
Years of services for reduced benefit	10 years
Directors' Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Duration for benefit payment after retirement age	10 years
Retirement age	65 years
Reduced benefit age	55 years
Years of services for reduced benefit	10 years
Directors' Retirement Plan [Member] | Minimum [Member]
Defined Benefit Plan Disclosure [Line Items]
Directors' retirement benefit per year of service	$ 1
Directors' Retirement Plan [Member] | Maximum [Member]
Defined Benefit Plan Disclosure [Line Items]
Directors' retirement benefit per year of service	$ 15