Employee Benefit Plans - Fair Value Measurements (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets		$ 41		$ 0
Defined Benefit Plan, Settlements, Plan Assets		0		(150)
Defined Benefit Plan, Fair Value of Plan Assets		666		662		$ 858
Domestic Other Postretirement Plans [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	411		401
Domestic Other Postretirement Plans [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	95		103
Domestic Other Postretirement Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		20	[2]	13
Domestic Other Postretirement Plans [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	18	[2]	12
Domestic Other Postretirement Plans [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	2	[2]	1
Domestic Other Postretirement Plans [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0	[2]	0
Domestic Other Postretirement Plans [Member] | US Treasury Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		19		18
Domestic Other Postretirement Plans [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	19		18
Domestic Other Postretirement Plans [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | US Treasury Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		29		33
Domestic Other Postretirement Plans [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	29		33
Domestic Other Postretirement Plans [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Municipal Bonds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		39		41
Domestic Other Postretirement Plans [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	39		41
Domestic Other Postretirement Plans [Member] | Municipal Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | US Government-sponsored Enterprises Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		25		28
Domestic Other Postretirement Plans [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	25		28
Domestic Other Postretirement Plans [Member] | US Government-sponsored Enterprises Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Domestic Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		217		216
Domestic Other Postretirement Plans [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	217		216
Domestic Other Postretirement Plans [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Domestic Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Foreign Equity Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		5		6
Domestic Other Postretirement Plans [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	5		6
Domestic Other Postretirement Plans [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Foreign Equity Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1]	0		0
Domestic Other Postretirement Plans [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	$ 152		$ 149
Percentage of Investment Funds Comprised Of Equity Securitites		63.00%		37.00%
Percentage of Investment Funds Comprised Of Debt Securities		37.00%		63.00%
Percentage Of Investment Funds Invested in United States Securities		72.00%		70.00%
Percentage Of Investment Funds Invested In International Securities		28.00%		30.00%
Domestic Other Postretirement Plans [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[3]	$ 152		$ 149
Domestic Other Postretirement Plans [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[3]	0		0
Domestic Other Postretirement Plans [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[1],[3]	0		0
Domestic Other Postretirement Plans [Member] | Plan Asset Categories Excluding Investments Measured with a NAV excluding the Practical Expedient [Domain]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		506		504
UK Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Actual Return on Plan Assets		349		48
Defined Benefit Plan, Fair Value of Plan Assets		2,169		2,276		2,368
UK Pension Plans [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	722		494
UK Pension Plans [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	1,178		1,388
UK Pension Plans [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	105		204
UK Pension Plans [Member] | Cash Equivalents [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		87		46
UK Pension Plans [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	4		46
UK Pension Plans [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	83		0
UK Pension Plans [Member] | Cash Equivalents [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0		0
UK Pension Plans [Member] | United Kingdom Government Obligations [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		718		424
UK Pension Plans [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		718	[4]	424
UK Pension Plans [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0	[4]	0
UK Pension Plans [Member] | United Kingdom Government Obligations [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		0	[4]	0
UK Pension Plans [Member] | Foreign Government Debt, Excluding That Of The United Kingdom [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets				13
UK Pension Plans [Member] | Foreign Government Debt, Excluding That Of The United Kingdom [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]			0
UK Pension Plans [Member] | Foreign Government Debt, Excluding That Of The United Kingdom [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]			13
UK Pension Plans [Member] | Foreign Government Debt, Excluding That Of The United Kingdom [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]			0
UK Pension Plans [Member] | Corporate Debt Securities [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets				186
UK Pension Plans [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]			0
UK Pension Plans [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]			186
UK Pension Plans [Member] | Corporate Debt Securities [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]			0
UK Pension Plans [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[5]	$ 1,095		1,213
Percentage of Investment Funds Comprised Of Equity Securitites		44.00%
Percentage of Investment Funds Comprised Of Debt Securities		56.00%
UK Pension Plans [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4],[5]	$ 0		24
UK Pension Plans [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4],[5]	1,095		1,189
UK Pension Plans [Member] | Equity Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4],[5]	0		0
UK Pension Plans [Member] | Real Estate Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		105		204
UK Pension Plans [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 1 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0		0
UK Pension Plans [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 2 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[4]	0		0
UK Pension Plans [Member] | Real Estate Funds [Member] | Fair Value, Inputs, Level 3 [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		105	[4]	204	[4]	$ 199	$ 179
UK Pension Plans [Member] | Plan Asset Categories Excluding Investments Measured with a NAV excluding the Practical Expedient [Domain]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2,005		2,086
Accounting Standards Update 2015-07 [Member] | Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		666		662
Accounting Standards Update 2015-07 [Member] | Domestic Other Postretirement Plans [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[3]	156		154
Accounting Standards Update 2015-07 [Member] | Domestic Other Postretirement Plans [Member] | Limited Partnership Interests [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[2]	4		4
Accounting Standards Update 2015-07 [Member] | UK Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets		2,169		2,276
Accounting Standards Update 2015-07 [Member] | UK Pension Plans [Member] | Equity Funds [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plan, Fair Value of Plan Assets	[5]	$ 164		$ 190

[1] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[2] Limited partnership interests include several funds that invest primarily in real estate, buyout, growth equity and venture capital.

[3] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 63% and 37%, respectively, for both 2016 and 2015. Additionally, these funds are invested in United States and international securities of approximately 72% and 28%, respectively, for 2016 and 70% and 30%, respectively, for 2015.

[4] Refer to Note 15 for additional discussion regarding the three levels of the fair value hierarchy.

[5] Investment funds are comprised of mutual funds and collective trust funds. These funds consist of equity and debt securities of approximately 44% and 56%, respectively, for both 2016 and 2015.