Pension and Postretirement Benefit Plans - Fair Value of Pension 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		$ 1,584	$ 1,505
Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		1,513	1,454		$ 1,493
Net Asset Value		533	745
Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		71	51		$ 40
Fair Value, Inputs, Level 1 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		69	102
Fair Value, Inputs, Level 1 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		0	0
Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		911	607
Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		38	35
Fair Value, Inputs, Level 3 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		33	16
Equity Securities [Member] | US All Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	62	76
Equity Securities [Member] | US All Cap [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[1]	62	76
Equity Securities [Member] | US Large Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		61	102
Equity Securities [Member] | US Large Cap [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value		61	102
Equity Securities [Member] | US Small Cap [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		7	26
Equity Securities [Member] | US Small Cap [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		7	26
Equity Securities [Member] | EAFE Composite [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		65	119
Equity Securities [Member] | EAFE Composite [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value		65	119
Equity Securities [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		52	66
Equity Securities [Member] | Emerging Markets [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value		52	66
Equity Securities [Member] | Emerging Markets [Member] | Fair Value, Inputs, Level 1 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets
Fixed Income Securities [Member] | Emerging Markets [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		82	65
Fixed Income Securities [Member] | Emerging Markets [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value		82	65
Fixed Income Securities [Member] | US Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	61	137
Fixed Income Securities [Member] | US Bonds [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value	[2]		70
Fixed Income Securities [Member] | US Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[2]	61	67
Fixed Income Securities [Member] | Corporate Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		464	419
Fixed Income Securities [Member] | Corporate Bonds [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value		238	221
Fixed Income Securities [Member] | Corporate Bonds [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		226	198
Fixed Income Securities [Member] | US Treasury Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		281	269
Fixed Income Securities [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		281	269
Fixed Income Securities [Member] | Foreign Government Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		26	25
Fixed Income Securities [Member] | Foreign Government Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		26	25
Alternative Investment [Member] | Hedge Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[3]		66
Alternative Investment [Member] | Hedge Funds [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value	[3]		66
Alternative Investment [Member] | Insurance Contracts [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	33	16
Alternative Investment [Member] | Insurance Contracts [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[4]	33	16
Real Estate [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		35	36
Real Estate [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Net Asset Value		35	36
Other securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	1	10
Other securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	(10)	1
Other securities [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets	[5]	11	9
Other securities [Member] | Fair Value, Inputs, Level 3 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets				[5]
Other securities [Member] | Interest Rate Contract [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		(10)	1
Cash and Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		354	73
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | UNITED STATES
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		353	72
Cash and Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member] | Pension Plan [Member] | Foreign Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Fair value of plan assets		$ 1	$ 1

[1] This category comprises a combination of small-, mid- and large-cap equity stocks that are allocated at the investment manager's discretion. Investments include common and preferred securities as well as equity funds that invest in these instruments.

[2] This category represents a combination of high-yield and investment grade corporate bonds, sovereign bonds, Yankee bonds, asset-backed securities and U.S. government bonds. Investments include fixed income funds that invest in these instruments.

[3] This category includes fund managers that invest in a well-diversified group of hedge funds where strategies include, but are not limited to, event driven, relative value, long/short market neutral, multistrategy and global macro. Investments may be made directly or through pooled funds.

[4] This category comprises contracts placed with insurance companies where the underlying assets are invested in fixed interest securities.

[5] Other assets in the U.S. represent interest rate derivatives which had a market value of $(10) at December 31, 2017 and $1 at December 31, 2016.