Employee Benefits (Details) £ in Millions, $ in Millions	3 Months Ended			9 Months Ended
	Sep. 30, 2016 GBP (£)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)
U.K. [Member]
Defined Benefit Plan Disclosure
Service cost		$ 0	$ 0	$ 0	$ 0
Interest cost		37	50	123	149
Expected return on plan assets, net of administration expenses		(58)	(77)	(187)	(229)
Amortization of prior-service cost		0	0	1	0
Amortization of net actuarial loss		7	11	24	31
Net periodic (benefit) cost		(14)	(16)	(39)	(49)
Loss on pension settlement		0	0	61	0
Curtailment gain and other		0	0	0	0
Total net periodic cost (benefit)		(14)	(16)	22	(49)
Lump sum payment	£ 116	159
Projected benefit obligation	103	141
Settlement	£ 42	61
Estimate of contributions to defined benefit pension plans for the current fiscal year		79		79
Contributions made to defined benefit pension plans		19	16	53	50
U.S. [Member]
Defined Benefit Plan Disclosure
Service cost		0	0	0	2
Interest cost		28	33	83	99
Expected return on plan assets, net of administration expenses		(39)	(38)	(117)	(115)
Amortization of prior-service cost		1	0	2	0
Amortization of net actuarial loss		12	14	37	41
Net periodic (benefit) cost		2	9	5	27
Loss on pension settlement		0	0	0	0
Curtailment gain and other		0	0	0	(1)
Total net periodic cost (benefit)		2	9	5	26
Estimate of contributions to defined benefit pension plans for the current fiscal year		54		54
Contributions made to defined benefit pension plans		5	41	24	103
Other [Member]
Defined Benefit Plan Disclosure
Service cost		0	0	0	0
Interest cost		7	8	21	25
Expected return on plan assets, net of administration expenses		(12)	(12)	(36)	(37)
Amortization of prior-service cost		0	0	0	0
Amortization of net actuarial loss		3	2	8	8
Net periodic (benefit) cost		(2)	(2)	(7)	(4)
Loss on pension settlement		0	0	0	0
Curtailment gain and other		0	0	0	0
Total net periodic cost (benefit)		(2)	(2)	(7)	(4)
Estimate of contributions to defined benefit pension plans for the current fiscal year		17		17
Contributions made to defined benefit pension plans		$ 4	$ 3	$ 14	$ 11