Income Taxes - Tax Credit and Loss Carryforwards (Details) - USD ($) $ in Millions	Dec. 31, 2019	Dec. 31, 2018
Operating Loss Carryforwards [Line Items]
Tax capital loss/credit carryforward	$ 73	$ 34
Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards not subject to expiration	5,882
Net operating loss carryforwards	9,591	9,319
State and Local Jurisdiction
Operating Loss Carryforwards [Line Items]
Net operating loss carryforwards not subject to expiration	362
Net operating loss carryforwards	2,849	2,244
Capital loss carryforwards | Internal Revenue Service (IRS)
Operating Loss Carryforwards [Line Items]
Tax capital loss/credit carryforward	$ 17	$ 0