Employee Benefits - Reconciliation of the changes in the benefit obligations and fair value of assets and a statement of the funded status (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
U.K. [Member]
Change in projected benefit obligation
Balance at the beginning of the Period	$ 5,106	$ 4,944
Service cost	1	1	1
Interest cost	230	210	217
Participant contributions	0	0
Plan amendment	0	0
Curtailments	0	0
Plan transfer and acquisitions	0	0
Actuarial loss (gain)	(211)	145
Benefit payments	(192)	(186)
Actual expenses	0	0
Change in discount rate	902	(95)
Foreign currency impact	(307)	87
Balance at the end of the period	5,529	5,106	4,944
Accumulated benefit obligation at end of year	5,529	5,106
Change in fair value of plan assets
Balance at the beginning of the period	5,398	4,860
Actual return on plan assets	1,199	304
Participant contributions	0	0
Employer contributions	166	316
Plan transfer and acquisitions	0	0
Benefit payments	(192)	(186)
Actual expenses	0	0
Foreign currency impact	(347)	104
Balance at the end of the period	6,224	5,398	4,860
Market related value at end of year	6,224	5,398
Funded status	695	292
Unrecognized prior-service cost	22	24
Unrecognized loss	1,687	2,012
Net amount recognized	2,404	2,328
U.S. [Member]
Change in projected benefit obligation
Balance at the beginning of the Period	2,744	2,884
Service cost	2	7	0
Interest cost	129	114	119
Participant contributions	0	0
Plan amendment	0	12
Curtailments	0	0
Plan transfer and acquisitions	13	115
Actuarial loss (gain)	265	17
Benefit payments	(130)	(128)
Actual expenses	0	0
Change in discount rate	327	(277)
Foreign currency impact	0	0
Balance at the end of the period	3,350	2,744	2,884
Accumulated benefit obligation at end of year	3,350	2,744
Change in fair value of plan assets
Balance at the beginning of the period	1,855	1,631
Actual return on plan assets	190	199
Participant contributions	0	0
Employer contributions	121	153
Plan transfer and acquisitions	0	0
Benefit payments	(130)	(128)
Actual expenses	0	0
Foreign currency impact	0	0
Balance at the end of the period	2,036	1,855	1,631
Market related value at end of year	1,950	1,765
Funded status	(1,314)	(889)
Unrecognized prior-service cost	11	12
Unrecognized loss	1,737	1,219
Net amount recognized	434	342
Other [Member]
Change in projected benefit obligation
Balance at the beginning of the Period	1,252	1,323
Service cost	0	18	14
Interest cost	47	45	48
Participant contributions	0	1
Plan amendment	0	0
Curtailments	(16)	(1)
Plan transfer and acquisitions	0	0
Actuarial loss (gain)	(5)	1
Benefit payments	(51)	(44)
Actual expenses	(2)	(1)
Change in discount rate	324	(85)
Foreign currency impact	(150)	(5)
Balance at the end of the period	1,399	1,252	1,323
Accumulated benefit obligation at end of year	1,316	1,177
Change in fair value of plan assets
Balance at the beginning of the period	1,061	1,009
Actual return on plan assets	253	34
Participant contributions	0	1
Employer contributions	28	55
Plan transfer and acquisitions	0	0
Benefit payments	(51)	(44)
Actual expenses	(2)	(1)
Foreign currency impact	(128)	7
Balance at the end of the period	1,161	1,061	1,009
Market related value at end of year	1,161	1,061
Funded status	(238)	(191)
Unrecognized prior-service cost	3	3
Unrecognized loss	456	402
Net amount recognized	$ 221	$ 214