Pension and Other Postretirement Benefits - Schedule of Fair Value of Pension Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Defined Benefit Plan Disclosure [Line Items]
Net receivables which represents assets related to divested businesses to be transferred to the buyers	$ 1	$ 28
Pension benefits paid
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	4,334	4,862	$ 4,666
Defined benefit plan, alternative investments, fair value of plan asset	2,726	2,932
Net plan assets, excluding net receivables from securities purchased and sold but not yet settled plus interest and dividends earned on various investments	4,333
Net plan assets excluding certain net receivables		4,834
Pension benefits paid | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,275	1,357
Defined benefit plan, alternative investments, fair value of plan asset	957	978
Pension benefits paid | Equities | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	896	972
Defined benefit plan, alternative investments, fair value of plan asset	578	593
Pension benefits paid | Equities | Long/short equity hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	232	230
Defined benefit plan, alternative investments, fair value of plan asset	232	230
Pension benefits paid | Equities | Private equity
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	147	155
Defined benefit plan, alternative investments, fair value of plan asset	147	155
Pension benefits paid | Fixed income
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	2,074	2,278
Defined benefit plan, alternative investments, fair value of plan asset	922	924
Pension benefits paid | Fixed income | Intermediate and long duration government/credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	1,904	1,961
Defined benefit plan, alternative investments, fair value of plan asset	770	779
Pension benefits paid | Fixed income | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	170	317
Defined benefit plan, alternative investments, fair value of plan asset	152	145
Pension benefits paid | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	984	1,199
Defined benefit plan, alternative investments, fair value of plan asset	847	1,030
Pension benefits paid | Other investments | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	268	359
Defined benefit plan, alternative investments, fair value of plan asset	212	275
Pension benefits paid | Other investments | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	245	257
Defined benefit plan, alternative investments, fair value of plan asset	164	172
Pension benefits paid | Other investments | Discretionary and systematic macro hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	471	583
Defined benefit plan, alternative investments, fair value of plan asset	471	583
Pension benefits paid | Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	664	906
Pension benefits paid | Level 1 | Equities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	318	379
Pension benefits paid | Level 1 | Equities | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	318	379
Pension benefits paid | Level 1 | Equities | 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 | Equities | 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	209	365
Pension benefits paid | Level 1 | Fixed income | Intermediate and long duration government/credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	200	201
Pension benefits paid | Level 1 | Fixed income | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	9	164
Pension benefits paid | Level 1 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	137	162
Pension benefits paid | Level 1 | Other investments | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	56	77
Pension benefits paid | Level 1 | Other investments | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	81	85
Pension benefits paid | Level 1 | Other investments | 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
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	943	996
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 | Equities | Equity securities
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Equities | 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 | Equities | 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	943	989
Pension benefits paid | Level 2 | Fixed income | Intermediate and long duration government/credit
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	934	981
Pension benefits paid | Level 2 | Fixed income | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	9	8
Pension benefits paid | Level 2 | Other investments
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	7
Pension benefits paid | Level 2 | Other investments | Other
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	7
Pension benefits paid | Level 2 | Other investments | Real estate
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	0	0
Pension benefits paid | Level 2 | Other investments | Discretionary and systematic macro hedge funds
Defined Benefit Plan Disclosure [Line Items]
Fair value of pension and other postretirement plans' assets	$ 0	$ 0