Income Taxes - Operating Loss and Tax Credit Carryforwards, Domestic, By Expiration Dates (Details) $ in Millions	Dec. 31, 2016 USD ($)
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | 2017 through 2021 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	$ 62
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | 2022 through 2026 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	36
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | 2027 through 2031 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	8
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | 2032 through 2036 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	76
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | 2037 through 2041 [Member] | 2037 through 2041 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	0
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Not subject to expiration [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	0
Domestic Tax Authority [Member] | Internal Revenue Service (IRS) [Member] | Valuation allowance [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal income tax credit carryforwards	(44)
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2017 through 2021 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	0
United States federal deferred income tax assets for income tax loss carryforwards	0
United States federal income tax credit carryforwards	62
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2017 through 2021 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	0
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2022 through 2026 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	15
United States federal deferred income tax assets for income tax loss carryforwards	5
United States federal income tax credit carryforwards	36
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2022 through 2026 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	5
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2027 through 2031 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	20
United States federal deferred income tax assets for income tax loss carryforwards	7
United States federal income tax credit carryforwards	39
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2027 through 2031 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	7
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2032 through 2036 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	618
United States federal deferred income tax assets for income tax loss carryforwards	172
United States federal income tax credit carryforwards	115
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2032 through 2036 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	39
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2037 through 2041 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	0
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2037 through 2041 [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	0
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | 2037 through 2041 [Member] | 2037 through 2041 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	0
United States federal income tax credit carryforwards	0
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | Not subject to expiration [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	0
United States federal deferred income tax assets for income tax loss carryforwards	0
United States federal income tax credit carryforwards	29
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | Not subject to expiration [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	0
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | Valuation allowance [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
Operating Loss Carryforwards	0
United States federal deferred income tax assets for income tax loss carryforwards	(12)
United States federal income tax credit carryforwards	(44)
Internal Revenue Service (IRS) [Member] | Domestic Tax Authority [Member] | Valuation allowance [Member] | After ASU 2013-11 [Member]
Operating Loss and Tax Credit Carry Forward [Line Items]
United States federal deferred income tax assets for income tax loss carryforwards	$ (12)