Income Taxes - Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect, By Expiration Dates (Details) - Domestic Tax Authority [Member] - State and Local Jurisdiction [Member] $ in Millions	Dec. 31, 2016 USD ($)
2017 through 2021 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	$ 8
2022 through 2026 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	17
2027 through 2031 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	11
2032 through 2036 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	8
2037 through 2041 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	0
Not subject to expiration [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	0
Related valuation allowance [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	(17)
2017 through 2021 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	11
2017 through 2021 [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	0
United States and local income tax credit carryforwards - net of federal tax effect	8
2022 through 2026 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	11
2022 through 2026 [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	12
United States and local income tax credit carryforwards - net of federal tax effect	11
2027 through 2031 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	7
2027 through 2031 [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	11
United States and local income tax credit carryforwards - net of federal tax effect	6
2032 through 2036 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	4
2032 through 2036 [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	8
United States and local income tax credit carryforwards - net of federal tax effect	2
2037 through 2041 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	5
2037 through 2041 [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	0
United States and local income tax credit carryforwards - net of federal tax effect	5
Not subject to expiration [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	0
Not subject to expiration [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	0
United States and local income tax credit carryforwards - net of federal tax effect	0
Related valuation allowance [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
United States and local income tax credit carryforwards - net of federal tax effect	(17)
Related valuation allowance [Member] | After ASU 2013-11 [Member]
Income Tax Loss and Tax Credit Carryforwards, State and Local, Net of Federal Tax Effect [Line Items]
Deferred Tax Assets, Operating Loss Carryforwards, State and Local	(17)
United States and local income tax credit carryforwards - net of federal tax effect	$ (17)