Income Taxes - Total Income Tax Expense (Benefit) and Resulting Effective Tax Rate (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Amount
Income (loss) before income taxes times 21% statutory federal tax rate	$ 683	$ 327	$ 425
Amortization of tax-advantaged investments	151	150	132
Tax-exempt interest income	(26)	(28)	(30)
Corporate-owned life insurance income	(27)	(29)	(29)
State income tax, net of federal tax benefit	79	37	31
Tax credits	(218)	(218)	(231)
Other	0	(12)	16
Total income tax expense (benefit)	$ 642	$ 227	$ 314
Rate
Federal income tax rate (as a percent)	21.00%	21.00%	21.00%
Amortization of tax-advantaged investments (as a percent)	4.60%	9.70%	6.50%
Tax-exempt interest income (as a percent)	(0.80%)	(1.80%)	(1.50%)
Corporate-owned life insurance income (as a percent)	(0.80%)	(1.90%)	(1.40%)
State income tax, net of federal tax benefit (as a percent)	2.40%	2.40%	1.50%
Tax credits (as a percent)	(6.70%)	(14.00%)	(11.40%)
Other (as a percent)	0.00%	(0.80%)	0.90%
Total income tax expense (benefit) (as a percent)	19.70%	14.60%	15.60%