Employee Benefit Plans - Employer Contributions (Details) - 3 months ended Mar. 31, 2016 £ in Millions, $ in Millions	USD ($)	GBP (£)
Domestic Pension Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year	$ 34
Employer contributions	3
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year	1
UK Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year | £		£ 40
Employer contributions	$ 17	£ 12