Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Defined Benefit Plan Disclosure [Line Items]
Net receivables which represents assets related to divested businesses to be transferred to the buyers		$ 1
Net payables which represents assets related to divested businesses to be transferred to the buyers	$ 7
Pension benefits paid
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	4,868	4,334	$ 4,862
Defined benefit plan, alternative investments, fair value of plan asset	2,880	2,726
Net plan assets excluding certain net receivables	4,875	4,333
Pension benefits paid | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,513	1,275
Defined benefit plan, alternative investments, fair value of plan asset	923	957
Pension benefits paid | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,098	896
Defined benefit plan, alternative investments, fair value of plan asset	508	578
Pension benefits paid | Long/short equity hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	260	232
Defined benefit plan, alternative investments, fair value of plan asset	260	232
Pension benefits paid | Private equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	155	147
Defined benefit plan, alternative investments, fair value of plan asset	155	147
Pension benefits paid | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	2,448	2,074
Defined benefit plan, alternative investments, fair value of plan asset	1,147	922
Pension benefits paid | Intermediate and long duration government/credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	2,171	1,904
Defined benefit plan, alternative investments, fair value of plan asset	1,003	770
Pension benefits paid | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	277	170
Defined benefit plan, alternative investments, fair value of plan asset	144	152
Pension benefits paid | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	914	984
Defined benefit plan, alternative investments, fair value of plan asset	810	847
Pension benefits paid | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	269	245
Defined benefit plan, alternative investments, fair value of plan asset	165	164
Pension benefits paid | Discretionary and systematic macro hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	405	471
Defined benefit plan, alternative investments, fair value of plan asset	405	471
Pension benefits paid | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	240	268
Defined benefit plan, alternative investments, fair value of plan asset	240	212
Pension benefits paid | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	941	664
Pension benefits paid | Level 1 | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	590	318
Pension benefits paid | Level 1 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	590	318
Pension benefits paid | Level 1 | Long/short equity hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 1 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 1 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	247	209
Pension benefits paid | Level 1 | Intermediate and long duration government/credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	121	200
Pension benefits paid | Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	126	9
Pension benefits paid | Level 1 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	104	137
Pension benefits paid | Level 1 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	104	81
Pension benefits paid | Level 1 | Discretionary and systematic macro hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 1 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	56
Pension benefits paid | Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,054	943
Pension benefits paid | Level 2 | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Long/short equity hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Private equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,054	943
Pension benefits paid | Level 2 | Intermediate and long duration government/credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,047	934
Pension benefits paid | Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	7	9
Pension benefits paid | Level 2 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Discretionary and systematic macro hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	$ 0	$ 0