Pension and Other Postretirement Benefits (Components of Net Periodic Benefit Cost and Amounts Recognized in Other Comprehensive Income (Loss) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Components of net periodic cost:
Settlements	$ 0	$ 0	$ 352
Other comprehensive income (loss):
Deferred income taxes	44	23	(90)
Recognized in other comprehensive income (loss), net of tax	(145)	(61)	73
Discontinued Operations [Member]
Components of net periodic cost:
Net periodic cost			3
Pension benefits [Member]
Components of net periodic cost:
Service cost	28	30	28
Interest cost	191	180	219
Expected return on plan assets	(183)	(214)	(230)
Amortization of actuarial losses (gains)	94	87	105
Amortization of prior service cost	1	1	1
Settlements	0	0	352
Net periodic cost	131	84	475
Other comprehensive income (loss):
Actuarial (loss) gain	(246)	(179)	(269)
Amortization of actuarial losses (gains)	94	87	105
Amortization of prior service cost	1	1	1
Settlements	0	0	352
Recognized in other comprehensive income, before tax	(151)	(91)	189
Deferred income taxes	37	25	(94)
Recognized in other comprehensive income (loss), net of tax	(114)	(66)	95
Expected Amortization
Estimated net actuarial gain (loss) that will be amortized into net periodic benefit cost over next fiscal year	(103)
Estimated net prior service cost (credit) that will be amortized into net periodic benefit cost over the next fiscal year	1
Postretirement benefits [Member]
Components of net periodic cost:
Service cost	1	1	1
Interest cost	16	17	19
Expected return on plan assets	0	0	0
Amortization of actuarial losses (gains)	(18)	(18)	(22)
Amortization of prior service cost	1	1	1
Settlements	0	0	0
Net periodic cost	0	1	(1)
Other comprehensive income (loss):
Actuarial (loss) gain	(9)	8	(20)
Amortization of actuarial losses (gains)	(18)	(18)	(22)
Amortization of prior service cost	1	1	1
Settlements	0	0	0
Recognized in other comprehensive income, before tax	(26)	(9)	(41)
Deferred income taxes	5	2	13
Recognized in other comprehensive income (loss), net of tax	(21)	$ (7)	$ (28)
Expected Amortization
Estimated net actuarial gain (loss) that will be amortized into net periodic benefit cost over next fiscal year	$ 15