Income Taxes - Tax Effected Operating Loss, Capital Loss, and Tax Credit Carryovers (Details) - USD ($) $ in Millions	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Income tax
Net UTB impacting the effective tax rate	$ 1,107		$ 1,178
Deferred tax assets valuation allowance	$ 158		$ 158
Effective tax rate (as a percent)	17.40%	17.90%
Increase (decrease) in effective income tax rate from prior reporting period to current reporting period (as a percent)	(0.50%)
Decrease in unrecognized tax benefits due to resolution of a lawsuit	$ 52