Retirement Plans (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 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	$ 21	$ 24	$ 43	$ 48
Interest cost	36	40	71	80
Expected return on plan assets	(67)	(64)	(134)	(128)
Amortization of actuarial loss	21	26	41	52
Net periodic pension/OPEB cost	11	26	21	52
Voluntary cash contributions to qualified pension plan			40
OPEB [Member]
Net Periodic Pension And OPEB Cost/(Benefit) [Abstract]
Service cost			1	1
Interest cost	3	4	6	7
Amortization of prior service credit	(3)	(3)	(5)	(5)
Amortization of actuarial loss	3	3	5	6
Net periodic pension/OPEB cost	$ 3	$ 4	$ 7	$ 9