Employee Benefits - Schedule of changes in Level 3 fair value for U.K. Pension Plans (Details) (U.K. [Member], USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013
Change in fair value of plan assets
Balance at the beginning of the period	$ 5,398		$ 4,860
Actual return on plan assets:
Foreign exchange	(347)		104
Balance at the end of the period	6,224		5,398
Global [Member]
Actual return on plan assets:
Balance at the end of the period	203	[1]	668	[1]
Annuities [Member]
Actual return on plan assets:
Balance at the end of the period	836		564
Alternative investments [Member]
Actual return on plan assets:
Balance at the end of the period	968	[1],[2]	546	[1],[2]
Significant Unobservable Inputs (Level 3) [Member]
Change in fair value of plan assets
Balance at the beginning of the period	1,133		1,084
Actual return on plan assets:
Relating to assets still held at the end of the year	309		20
Relating to assets sold during the year	6		8
Purchases, sales and settlements—net	713		1
Transfer in/(out) of Level 3	(206)		0
Foreign exchange	(105)		20
Balance at the end of the period	1,850		1,133
Significant Unobservable Inputs (Level 3) [Member] | Global [Member]
Actual return on plan assets:
Balance at the end of the period	0	[1]	0	[1]
Significant Unobservable Inputs (Level 3) [Member] | Annuities [Member]
Change in fair value of plan assets
Balance at the beginning of the period	564		568
Actual return on plan assets:
Relating to assets still held at the end of the year	(13)		(13)
Relating to assets sold during the year	0		0
Purchases, sales and settlements—net	333		0
Transfer in/(out) of Level 3	0		0
Foreign exchange	(48)		9
Balance at the end of the period	836		564
Significant Unobservable Inputs (Level 3) [Member] | Pooled funds - Real estate [Member]
Change in fair value of plan assets
Balance at the beginning of the period	23		70
Actual return on plan assets:
Relating to assets still held at the end of the year	3		1
Relating to assets sold during the year	1		3
Purchases, sales and settlements—net	21		(50)
Transfer in/(out) of Level 3	0		0
Foreign exchange	(2)		(1)
Balance at the end of the period	46		23
Significant Unobservable Inputs (Level 3) [Member] | Alternative investments [Member]
Change in fair value of plan assets
Balance at the beginning of the period	546	[1],[2]	446
Actual return on plan assets:
Relating to assets still held at the end of the year	319		32
Relating to assets sold during the year	5		5
Purchases, sales and settlements—net	359		51
Transfer in/(out) of Level 3	(206)		0
Foreign exchange	(55)		12
Balance at the end of the period	$ 968	[1],[2]	$ 546	[1],[2]

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

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