Employee Benefits - Schedule of Fair Value of U.K. Plan Assets (Details) - U.K. [Member] - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 5,903	$ 6,224	$ 5,398
Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	159	224
Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	360	203
Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	17	16
Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	133	127
Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	66	0
Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	283	279
Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	3,145	3,292
Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	827	836
Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	111	233
Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	65	39
Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	717	968
Real Estate, Excluding Pooled Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	20	7
Quoted Prices in Active Markets for Identical Assets (Level 1)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	2,621	3,643
Quoted Prices in Active Markets for Identical Assets (Level 1) | Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	159	224
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	61	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	133	127
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	2,268	3,292
Quoted Prices in Active Markets for Identical Assets (Level 1) | Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Quoted Prices in Active Markets for Identical Assets (Level 1) | Real Estate, Excluding Pooled Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Significant Other Observable Inputs (Level 2)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,633	731
Significant Other Observable Inputs (Level 2) | Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	299	203
Significant Other Observable Inputs (Level 2) | Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	17	16
Significant Other Observable Inputs (Level 2) | Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	66	0
Significant Other Observable Inputs (Level 2) | Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	259	279
Significant Other Observable Inputs (Level 2) | Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	877	0
Significant Other Observable Inputs (Level 2) | Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	111	233
Significant Other Observable Inputs (Level 2) | Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Other Observable Inputs (Level 2) | Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	4	0
Significant Other Observable Inputs (Level 2) | Real Estate, Excluding Pooled Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		0
Significant Unobservable Inputs (Level 3)
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,649	1,850	1,133
Significant Unobservable Inputs (Level 3) | Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	24	0
Significant Unobservable Inputs (Level 3) | Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	827	836	564
Significant Unobservable Inputs (Level 3) | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	0
Significant Unobservable Inputs (Level 3) | Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	65	39
Significant Unobservable Inputs (Level 3) | Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	713	968	$ 546
Significant Unobservable Inputs (Level 3) | Real Estate, Excluding Pooled Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 20	$ 7