Pension and Other Postretirement Benefits - Benefit Costs (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Net periodic benefit costs included in the statement of income
Income from continuing operations									$ 2,035	$ 1,899	$ 1,890
Income from Discontinued Operations									0	0	1,056
Net Income	$ 507	$ 535	$ 525	$ 468	$ 450	$ 511	$ 480	$ 458	2,035	1,899	2,946
Pension
Components of net periodic benefit cost:
Service cost									62	70	80
Interest cost									92	92	103
Expected return on plan assets									(144)	(151)	(159)
Amortization of actuarial (gain) loss									44	60	48
Amortization of prior service cost									0	1	1
Settlement/curtailment (gain) loss									0	0	1
Total net periodic benefit cost									54	72	74
Net periodic benefit costs included in the statement of income
Income from continuing operations									54	72	69
Income from Discontinued Operations									0	0	5
Net Income									54	72	74
Other Postretirement Benefits
Components of net periodic benefit cost:
Service cost									9	11	10
Interest cost									24	24	24
Expected return on plan assets									(23)	(25)	(25)
Amortization of actuarial (gain) loss									0	(1)	(4)
Amortization of prior service cost									(1)	1	1
Settlement/curtailment (gain) loss									0	0	(9)
Total net periodic benefit cost									9	10	(3)
Net periodic benefit costs included in the statement of income
Income from continuing operations									9	10	6
Income from Discontinued Operations									0	0	(9)
Net Income									$ 9	$ 10	$ (3)