Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Net Periodic Pension And OPEB Cost/(Benefit) [Abstract]
Changes in fair value	5 years
Pension [Member]
Net Periodic Pension And OPEB Cost/(Benefit) [Abstract]
Service cost	$ 22	$ 24
Interest cost	35	40
Expected return on plan assets	(67)	(64)
Amortization of actuarial loss	20	26
Net periodic pension/OPEB cost	10	26
Voluntary cash contributions to qualified pension plan	10
OPEB [Member]
Net Periodic Pension And OPEB Cost/(Benefit) [Abstract]
Service cost	1	1
Interest cost	3	3
Amortization of prior service credit	(2)	(2)
Amortization of actuarial loss	2	3
Net periodic pension/OPEB cost	$ 4	$ 5