Employee Benefits - Amounts recognized in the Consolidated Statements of Financial Position (Details) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014		Dec. 31, 2013
U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	$ 918	[1]	$ 549	[1]
Accrued benefit liability	(223)	[2]	(257)	[2]
Accumulated other comprehensive loss	1,709		2,036
Net amount recognized	2,404		2,328
U.S. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	0	[1]	0	[1]
Accrued benefit liability	(1,314)	[2]	(889)	[2]
Accumulated other comprehensive loss	1,748		1,231
Net amount recognized	434		342
Other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	0	[1]	1	[1]
Accrued benefit liability	(238)	[2]	(192)	[2]
Accumulated other comprehensive loss	459		405
Net amount recognized	$ 221		$ 214

[1] Included in Other non-current assets

[2] Included in Pension, other post retirement, and post employment liabilities