Employee Benefits - Schedule of changes in Level 3 fair value for U.K. Pension Plans (Details) - U.K. [Member] - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Change in fair value of plan assets
Balance at the beginning of the period	$ 6,224	$ 5,398
Actual return on plan assets:
Foreign exchange	(257)	(347)
Balance at the end of the period	5,903	6,224
Global [Member]
Change in fair value of plan assets
Balance at the beginning of the period	203
Actual return on plan assets:
Balance at the end of the period	360	203
Annuities [Member]
Change in fair value of plan assets
Balance at the beginning of the period	836
Actual return on plan assets:
Balance at the end of the period	827	836
Alternative investments [Member]
Change in fair value of plan assets
Balance at the beginning of the period	968
Actual return on plan assets:
Balance at the end of the period	717	968
Pooled funds - Fixed income securities [Member]
Change in fair value of plan assets
Balance at the beginning of the period	279
Actual return on plan assets:
Balance at the end of the period	283	279
Significant Unobservable Inputs (Level 3)
Change in fair value of plan assets
Balance at the beginning of the period	1,850	1,133
Actual return on plan assets:
Relating to assets still held at the end of the year	(45)	309
Relating to assets sold during the year	(9)	6
Purchases, sales and settlements—net	168	713
Transfer in/(out) of Level 3	(242)	(206)
Foreign exchange	(73)	(105)
Balance at the end of the period	1,649	1,850
Significant Unobservable Inputs (Level 3) | Global [Member]
Change in fair value of plan assets
Balance at the beginning of the period	0
Actual return on plan assets:
Balance at the end of the period	0	0
Significant Unobservable Inputs (Level 3) | Annuities [Member]
Change in fair value of plan assets
Balance at the beginning of the period	836	564
Actual return on plan assets:
Relating to assets still held at the end of the year	(32)	(13)
Relating to assets sold during the year	0	0
Purchases, sales and settlements—net	58	333
Transfer in/(out) of Level 3	0	0
Foreign exchange	(35)	(48)
Balance at the end of the period	827	836
Significant Unobservable Inputs (Level 3) | Pooled funds - Real estate [Member]
Change in fair value of plan assets
Balance at the beginning of the period	46	23
Actual return on plan assets:
Relating to assets still held at the end of the year	11	3
Relating to assets sold during the year	(10)	1
Purchases, sales and settlements—net	41	21
Transfer in/(out) of Level 3	0	0
Foreign exchange	(3)	(2)
Balance at the end of the period	85	46
Significant Unobservable Inputs (Level 3) | Alternative investments [Member]
Change in fair value of plan assets
Balance at the beginning of the period	968	546
Actual return on plan assets:
Relating to assets still held at the end of the year	(17)	319
Relating to assets sold during the year	2	5
Purchases, sales and settlements—net	60	359
Transfer in/(out) of Level 3	(266)	(206)
Foreign exchange	(34)	(55)
Balance at the end of the period	713	968
Significant Unobservable Inputs (Level 3) | Pooled funds - Fixed income securities [Member]
Change in fair value of plan assets
Balance at the beginning of the period	0
Actual return on plan assets:
Relating to assets still held at the end of the year	(7)
Relating to assets sold during the year	(1)
Purchases, sales and settlements—net	9
Transfer in/(out) of Level 3	24
Foreign exchange	(1)
Balance at the end of the period	$ 24	$ 0