Goodwill and Other Intangible Assets (Details) - Other Intangible Assets - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Other intangible assets by major asset class
Intangible assets subject to amortization, gross carrying amount	$ 289		$ 286
Intangible assets subject to amortization, accumulated amortization	175		171
Intangible assets subject to amortization, net	114		115
Intangible assets not subject to amortization	227		227
Total other intangible assets, gross carrying amount	516		513
Total other intangible assets, net	341		342
Amortization expense of intangible assets	4	$ 3
Estimated intangible asset amortization expense, remainder of 2018	11
Estimated intangible asset amortization expense, 2019	14
Estimated intangible asset amortization expense, 2020	13
Estimated intangible asset amortization expense, 2021	12
Estimated intangible asset amortization expense, 2022	11
Customer-related [Member]
Other intangible assets by major asset class
Intangible assets subject to amortization, gross carrying amount	80		77
Intangible assets subject to amortization, accumulated amortization	5		4
Intangible assets subject to amortization, net	75		73
Contract-based [Member]
Other intangible assets by major asset class
Intangible assets subject to amortization, gross carrying amount	209		209
Intangible assets subject to amortization, accumulated amortization	170		167
Intangible assets subject to amortization, net	$ 39		$ 42