Goodwill (details) - Other Intangible Assets - USD ($) $ in Millions	Dec. 31, 2017	Dec. 31, 2016
Other intangible assets by major asset class
Intangible assets subject to amortization, gross carrying amount	$ 286	$ 210
Intangible assets subject to amortization, accumulated amortization	171	159
Intangible assets subject to amortization, net	115	51
Customer-related [Member]
Other intangible assets by major asset class
Intangible assets subject to amortization, gross carrying amount	77
Intangible assets subject to amortization, accumulated amortization	4
Intangible assets subject to amortization, net	73
Contract-based [Member]
Other intangible assets by major asset class
Intangible assets subject to amortization, gross carrying amount	209	210
Intangible assets subject to amortization, accumulated amortization	167	159
Intangible assets subject to amortization, net	$ 42	$ 51