Pension and Other Postretirement Employee Benefit Plans - Defined Benefit Pension Plans (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Defined Benefit Plan Disclosure [Line Items]
Defined Benefit Plans, Compensation Limit	$ 100,000
Defined benefit pension plan, benefit obligation expense retirement plan	257,000,000	245,000,000
Defined Contribution Plan:
Employer matching percent of employees' gross pay	5.00%
Employee annual compensation amount not eligible for employers matching contributions	250,000
Defined Benefit Pension Plans
Defined Benefit Plan Disclosure [Line Items]
Period after which employees begin to accrue plan benefits	1 year
Period after which benefits generally vest	3 years
Defined Contribution Plan:
Period after which employees begin to receive matching contributions	1 year
Period after which matching contributions vest for employees hired after May 1, 2009	3 years
Funded status of plan - supplemental information
Unfunded postretirement benefit obligation, U.K. Plan	37,000,000	34,000,000
U.S. defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, estimated future employer contributions in next fiscal year	0
Change in benefit obligation
Benefit obligation, beginning of year	(10,776,000,000)	(11,478,000,000)
Benefits earned during the year	(281,000,000)	(314,000,000)	(272,000,000)
Interest cost on benefit obligations	(534,000,000)	(447,000,000)	(466,000,000)
Plan amendments	(53,000,000)	0
Special termination benefits	0	0
Curtailments	0	0
Net gain/(loss)	(1,669,000,000)	794,000,000
Benefits paid	777,000,000	669,000,000
Foreign exchange impact and other	0	0
Benefit obligation, end of year	(12,536,000,000)	(10,776,000,000)	(11,478,000,000)
Change in plan assets
Fair value of plan assets, beginning of year	14,354,000,000	13,012,000,000
Actual return on plan assets	1,010,000,000	1,979,000,000
Firm contributions	36,000,000	32,000,000
Employee contributions	0	0
Benefits paid	(777,000,000)	(669,000,000)
Foreign exchange impact and other	0	0
Fair value of plan assets, end of year	14,623,000,000	14,354,000,000	13,012,000,000
Net funded status	2,087,000,000	3,578,000,000
Accumulated benefit obligation, end of year	(12,375,000,000)	(10,685,000,000)
U.S. defined benefit pension plans | Participation rights under participating annuity contracts
Change in plan assets
Fair value of plan assets, end of year	336,000,000	429,000,000
U.S. defined benefit pension plans | Accrued receivables
Funded status of plan - supplemental information
Defined benefit plans, amounts not measured at fair value	106,000,000	96,000,000
U.S. defined benefit pension plans | Accrued liabilities
Funded status of plan - supplemental information
Defined benefit plans, amounts not measured at fair value	257,000,000	104,000,000
Non-U.S. defined benefit pension plans
Defined Benefit Plan Disclosure [Line Items]
Defined benefit pension plan, estimated future employer contributions in next fiscal year	47,000,000
Defined benefit plan, contractually required future employer contributions in next fiscal year	31,000,000
Change in benefit obligation
Benefit obligation, beginning of year	(3,433,000,000)	(3,243,000,000)
Benefits earned during the year	(33,000,000)	(34,000,000)	(41,000,000)
Interest cost on benefit obligations	(137,000,000)	(125,000,000)	(126,000,000)
Plan amendments	0	0
Special termination benefits	(1,000,000)	0
Curtailments	0	0
Employee contributions	(7,000,000)	(7,000,000)
Net gain/(loss)	(408,000,000)	(62,000,000)
Benefits paid	119,000,000	106,000,000
Foreign exchange impact and other	260,000,000	(68,000,000)
Benefit obligation, end of year	(3,640,000,000)	(3,433,000,000)	(3,243,000,000)
Change in plan assets
Fair value of plan assets, beginning of year	3,532,000,000	3,330,000,000
Actual return on plan assets	518,000,000	187,000,000
Firm contributions	46,000,000	45,000,000
Employee contributions	7,000,000	7,000,000
Benefits paid	(119,000,000)	(106,000,000)
Foreign exchange impact and other	(266,000,000)	69,000,000
Fair value of plan assets, end of year	3,718,000,000	3,532,000,000	3,330,000,000
Net funded status	78,000,000	99,000,000
Accumulated benefit obligation, end of year	(3,615,000,000)	(3,406,000,000)
OPEB Plans
Change in benefit obligation
Benefit obligation, beginning of year	(826,000,000)	(990,000,000)
Benefits earned during the year	0	(1,000,000)	(1,000,000)
Interest cost on benefit obligations	(38,000,000)	(35,000,000)	(44,000,000)
Plan amendments	0	0
Special termination benefits	0	0
Curtailments	(3,000,000)	0
Employee contributions	(62,000,000)	(72,000,000)
Net gain/(loss)	(58,000,000)	138,000,000
Benefits paid	145,000,000	144,000,000
Expected Medicare Part D subsidy receipts	(2,000,000)	(10,000,000)
Foreign exchange impact and other	2,000,000	0
Benefit obligation, end of year	(842,000,000)	(826,000,000)	(990,000,000)
Change in plan assets
Fair value of plan assets, beginning of year	1,757,000,000	1,563,000,000
Actual return on plan assets	159,000,000	211,000,000
Firm contributions	3,000,000	2,000,000
Employee contributions	0	0
Benefits paid	(16,000,000)	(19,000,000)
Foreign exchange impact and other	0	0
Fair value of plan assets, end of year	1,903,000,000	1,757,000,000	1,563,000,000
Net funded status	1,061,000,000	931,000,000
OPEB Plans | Overfunded plans
Change in plan assets
Net funded status	3,900,000,000	5,100,000,000
OPEB Plans | Underfunded plans
Change in plan assets
Net funded status	$ 708,000,000	$ 540,000,000