Goodwill, Other Intangibles, and Property and Equipment - Depreciation and Amortization (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015		Dec. 31, 2014	Dec. 31, 2013
Depreciation And Amortization By Type [Line Items]
Depreciation And Amortization	$ 585		$ 588	$ 597
Benefit of a 2015 acquisition in which the fair value of acquired net assets exceeded the purchase price	23
Estimated pre-tax intangible asset amortization expense in 2016	432
Estimated pre-tax intangible asset amortization expense in 2017	313
Estimated pre-tax intangible asset amortization expense in 2018	216
Estimated pre-tax intangible asset amortization expense in 2019	151
Estimated pre-tax intangible asset amortization expense in 2020	82
Internal-use software [Member]
Depreciation And Amortization By Type [Line Items]
Depreciation And Amortization	288		260	225
Other property and equipment [Member]
Depreciation And Amortization By Type [Line Items]
Depreciation And Amortization	160		153	160
Assets Recorded under Capital Leases [Member]
Depreciation And Amortization By Type [Line Items]
Depreciation And Amortization	22		20
Other Intangibles [Member]
Depreciation And Amortization By Type [Line Items]
Depreciation And Amortization	119	[1]	163	193
Value Of Business Acquired [Member]
Depreciation And Amortization By Type [Line Items]
Depreciation And Amortization	$ 18		$ 12	$ 19

[1] Includes the one-time $23 million benefit of a 2015 acquisition in which the fair value of acquired net assets exceeded the purchase price.