Employee Benefits - Schedule of Fair Value of U.K. Plan Assets (Details) (U.K. [Member], USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 6,224		$ 5,398		$ 4,860
Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	224		555
Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	203	[1]	668	[1]
Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	16	[1]	155	[1]
Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	127	[2]	171	[2]
Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[2]	31	[2]
Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	279	[1]	500	[1]
Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	3,292	[3]	2,043	[3]
Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	836		564
Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	233	[3]	142	[3]
Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	39	[1],[4]	23	[1],[4]
Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	968	[1],[5]	546	[1],[5]
Real Estate, Excluding Pooled Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	7	[1],[4]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	3,643		2,769
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Cash and cash equivalents [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	224		555
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	127	[2]	171	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[2]	0	[2]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		[1]	0	[1]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	3,292	[3]	2,043	[3]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | 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) [Member] | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[3]	0	[3]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1],[4]	0	[1],[4]
Quoted Prices in Active Markets for Identical Assets (Level 1) [Member] | Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1],[5]	0	[1],[5]
Significant Other Observable Inputs (Level 2) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	731		1,496
Significant Other Observable Inputs (Level 2) [Member] | 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) [Member] | Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	203	[1]	668	[1]
Significant Other Observable Inputs (Level 2) [Member] | Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	16	[1]	155	[1]
Significant Other Observable Inputs (Level 2) [Member] | Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[2]	0	[2]
Significant Other Observable Inputs (Level 2) [Member] | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[2]	31	[2]
Significant Other Observable Inputs (Level 2) [Member] | Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	279	[1]	500	[1]
Significant Other Observable Inputs (Level 2) [Member] | Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total		[3]	0	[3]
Significant Other Observable Inputs (Level 2) [Member] | Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0		0
Significant Other Observable Inputs (Level 2) [Member] | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	233	[3]	142	[3]
Significant Other Observable Inputs (Level 2) [Member] | Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1],[4]	0	[1],[4]
Significant Other Observable Inputs (Level 2) [Member] | Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1],[5]	0	[1],[5]
Significant Unobservable Inputs (Level 3) [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	1,850		1,133		1,084
Significant Unobservable Inputs (Level 3) [Member] | 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) [Member] | Pooled funds - Global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Pooled funds - Europe [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Equity securities - global [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[2]	0	[2]
Significant Unobservable Inputs (Level 3) [Member] | Pooled funds - Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Fixed income securities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[3]	0	[3]
Significant Unobservable Inputs (Level 3) [Member] | Annuities [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	836		564		568
Significant Unobservable Inputs (Level 3) [Member] | Derivatives [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	0	[3]	0	[3]
Significant Unobservable Inputs (Level 3) [Member] | Pooled Funds, Real Estate [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	39	[1],[4]	23	[1],[4]
Significant Unobservable Inputs (Level 3) [Member] | Alternative investments [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	968	[1],[5]	546	[1],[5]	446
Significant Unobservable Inputs (Level 3) [Member] | Real Estate, Excluding Pooled Funds [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Total	$ 7	[1],[4]

[1] Consists of various equity, fixed income, commodity, and real estate mutual fund type investment vehicles.

[2] Consists of equity securities and equity derivatives.

[3] Consists of corporate and government bonds and fixed income derivatives.

[4] Consists of property funds and trusts holding direct real estate investments.

[5] Consists of limited partnerships, private equity and hedge funds.