Employee Benefits - Amounts recognized in Accumulated other comprehensive loss that have not yet been recognized (Details 3) (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
U.K. [Member]
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	$ 1,687	$ 2,012
Prior service cost	22	24
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost	1,709	2,036
U.S. [Member]
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	1,737	1,219
Prior service cost	11	12
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost	1,748	1,231
Other [Member]
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost
Net loss	456	402
Prior service cost	3	3
Amounts recognized in Accumulated other comprehensive loss unrecognized as components of net periodic benefit cost	$ 459	$ 405