Employee Benefits - Amounts recognized in the Consolidated Statements of Financial Position (Details) - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
U.K. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	$ 1,012	$ 918
Accrued benefit liability	(94)	(223)
Accumulated other comprehensive loss	1,511	1,709
Net amount recognized	2,429	2,404
U.S. [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	0	0
Accrued benefit liability	(1,209)	(1,314)
Accumulated other comprehensive loss	1,732	1,748
Net amount recognized	523	434
Other [Member]
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]
Prepaid benefit cost	0	0
Accrued benefit liability	(158)	(238)
Accumulated other comprehensive loss	382	459
Net amount recognized	$ 224	$ 221