Goodwill and Other Intangible Assets (Other Intangible Assets Narrative) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Gross	$ 18,000,000	$ 41,000,000
Finite-Lived Intangible Assets, Net	10,000,000	14,000,000
Indefinite-Lived Intangible Assets (Excluding Goodwill)	79,000,000	86,000,000
Capitalized Computer Software, Gross	1,200,000,000	1,300,000,000
Capitalized Computer Software, Net	416,000,000	574,000,000
Capitalized Computer Software, Development Stage Costs	32,000,000
Impairment of Long-Lived Assets Held-for-use	$ 2,123,000,000	1,919,000,000	$ 68,000,000
Finite-Lived Intangible Assets, Except Capitalized Internal-Use Software [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Weighted-Average Useful Life	6 years
Acquired Finite-lived Intangible Asset, Residual Value	$ 0
Amortization expense	4,000,000	14,000,000	15,000,000
Amortization expense for 2018	3,000,000
Amortization expense for 2019	1,000,000
Amortization expense for 2020	1,000,000
Amortization expense for 2021	1,000,000
Amortization expense for 2022	1,000,000
Amortization expense thereafter	3,000,000
Capitalized Internal Use Software [Member]
Finite-Lived Intangible Assets [Line Items]
Acquired Finite-lived Intangible Asset, Residual Value	0
Amortization expense	178,000,000	$ 201,000,000	$ 212,000,000
Amortization expense for 2018	153,000,000
Amortization expense for 2019	93,000,000
Amortization expense for 2020	69,000,000
Amortization expense for 2021	47,000,000
Amortization expense for 2022	33,000,000
Amortization expense thereafter	$ 21,000,000
Capitalized Internal Use Software, Except Significant System Conversions [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Weighted-Average Useful Life	3 years
Minimum [Member] | Capitalized Internal Use Software, Significant System Conversions [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Weighted-Average Useful Life	8 years
Maximum [Member] | Capitalized Internal Use Software, Significant System Conversions [Member]
Finite-Lived Intangible Assets [Line Items]
Finite-Lived Intangible Assets, Weighted-Average Useful Life	10 years