Pension Benefits Fair Value of Plan Assets (Details) - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 377	$ 1,212
Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	17	61
Time Deposits
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4	10
Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	114	423
Bond Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	94	469
Real Estate Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	13	29
Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	27	107
Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	6	5
Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	51	51
Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	51	57
Level 1
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	119	169
Level 1 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	17	61
Level 1 | Time Deposits
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 | Bond Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 | Real Estate Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 | Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 1 | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	51	51
Level 1 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	51	57
Level 2
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	212	902
Level 2 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 | Time Deposits
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	4	10
Level 2 | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	114	423
Level 2 | Bond Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	94	469
Level 2 | Real Estate Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 | Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 2 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	46	141
Level 3 | Cash
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 | Time Deposits
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 | Equity Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 | Bond Mutual Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 | Real Estate Trust Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	13	29	$ 39
Level 3 | Hedge Funds
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	27	107	102
Level 3 | Insurance Contracts
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	6	5	$ 1
Level 3 | Debt Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	0	0
Level 3 | Equity Securities
Defined Benefit Plan Disclosure [Line Items]
Fair Value of Plan Assets	$ 0	$ 0