Employee Benefits - Components of net periodic benefit cost (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	$ 1	$ 1	$ 1
Interest cost	230	210	217
Expected return on plan assets	(326)	(302)	(274)
Amortization of prior-service cost	1	1	1
Amortization of net actuarial loss	52	49	43
Curtailment loss (gain) and other	0	0	0
Net periodic benefit cost	(42)	(41)	(12)
U.S. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	2	7	0
Interest cost	129	114	119
Expected return on plan assets	(157)	(139)	(127)
Amortization of prior-service cost	2	0	0
Amortization of net actuarial loss	42	52	43
Curtailment loss (gain) and other	0	0	0
Net periodic benefit cost	18	34	35
Other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Service cost	0	18	14
Interest cost	47	45	48
Expected return on plan assets	(59)	(59)	(49)
Amortization of prior-service cost	0	0	0
Amortization of net actuarial loss	10	23	17
Curtailment loss (gain) and other	(2)	0	0
Net periodic benefit cost	$ (4)	$ 27	$ 30