Employee Benefits (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
U.K. [Member]
Defined Benefit Plan Disclosure
Service cost	$ 0	$ 0
Interest cost	43	49
Expected return on plan assets, net of administration expenses	(64)	(75)
Amortization of prior-service cost	1	0
Amortization of net actuarial loss	8	10
Net periodic (benefit) cost	(12)	(16)
Curtailment gain and other	0	0
Total net periodic (benefit) cost	(12)	(16)
Estimate of contributions to defined benefit pension plans for the current fiscal year	79
Contributions made to defined benefit pension plans	17	19
U.S. [Member]
Defined Benefit Plan Disclosure
Service cost	0	1
Interest cost	28	33
Expected return on plan assets, net of administration expenses	(39)	(39)
Amortization of prior-service cost	0	0
Amortization of net actuarial loss	13	14
Net periodic (benefit) cost	2	9
Curtailment gain and other	0	(1)
Total net periodic (benefit) cost	2	8
Estimate of contributions to defined benefit pension plans for the current fiscal year	54
Contributions made to defined benefit pension plans	13	34
Other [Member]
Defined Benefit Plan Disclosure
Service cost	0	0
Interest cost	7	8
Expected return on plan assets, net of administration expenses	(12)	(12)
Amortization of prior-service cost	0	0
Amortization of net actuarial loss	3	3
Net periodic (benefit) cost	(2)	(1)
Curtailment gain and other	0	0
Total net periodic (benefit) cost	(2)	(1)
Estimate of contributions to defined benefit pension plans for the current fiscal year	17
Contributions made to defined benefit pension plans	$ 7	$ 4