Employee Benefit Plans - Employer Contributions (Details) - 9 months ended Sep. 30, 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	$ 77
Employer contributions	73
Domestic Other Postretirement Plans [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year	1
Employer contributions	1
UK Pension Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Defined benefit plan, expected contributions in current fiscal year | £		£ 41
Employer contributions	$ 44	£ 31