Goodwill, Other Intangibles, and Property and Equipment - Property and Equipment (Details) - USD ($) $ in Millions		12 Months Ended
		Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Line Items]
Cost		$ 4,364	$ 4,016
Accumulated amortization		2,828	2,482
Net carrying value		$ 1,536	1,534
Capital lease agreements, term length		4 years
Internal-use software [Member]
Property Plant And Equipment [Line Items]
Cost		$ 2,766	2,442
Accumulated amortization		1,997	1,708
Net carrying value		769	734
Total other property and equipment [Member]
Property Plant And Equipment [Line Items]
Cost		1,598	1,574
Accumulated amortization		831	774
Net carrying value		767	800
Assets recorded under capital leases [Member]
Property Plant And Equipment [Line Items]
Cost	[1]	87	90
Accumulated amortization	[1]	49	44
Net carrying value	[1]	38	46
Other property and equipment not recorded under capital leases [Member]
Property Plant And Equipment [Line Items]
Cost		1,511	1,484
Accumulated amortization		782	730
Net carrying value		$ 729	$ 754

[1] Current capital lease agreements are for equipment and generally have a term of 48 months with the equipment expected to be returned to the lessor at termination.