Debt Securities (Composition of Debt Securities Portfolio in Unrealized Loss Position by Credit Rating Agencies) (Detail) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 7,646	$ 5,772
Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 6,953
Percentage of debt securities in unrealized loss position	90.90%
Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 541
Percentage of debt securities in unrealized loss position	7.10%
Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 152
Percentage of debt securities in unrealized loss position	2.00%
U.S. Treasury bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 158	76
U.S. Treasury bonds | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 158
Percentage of debt securities in unrealized loss position	100.00%
U.S. Treasury bonds | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Percentage of debt securities in unrealized loss position	0.00%
U.S. Treasury bonds | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Percentage of debt securities in unrealized loss position	0.00%
Municipal bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 1,353	684
Municipal bonds | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 1,315
Percentage of debt securities in unrealized loss position	97.20%
Municipal bonds | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 38
Percentage of debt securities in unrealized loss position	2.80%
Municipal bonds | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Percentage of debt securities in unrealized loss position	0.00%
Foreign government bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 188	136
Foreign government bonds | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 184
Percentage of debt securities in unrealized loss position	97.90%
Foreign government bonds | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 1
Percentage of debt securities in unrealized loss position	0.50%
Foreign government bonds | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 3
Percentage of debt securities in unrealized loss position	1.60%
Governmental agency bonds
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 229	73
Governmental agency bonds | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 229
Percentage of debt securities in unrealized loss position	100.00%
Governmental agency bonds | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Percentage of debt securities in unrealized loss position	0.00%
Governmental agency bonds | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Percentage of debt securities in unrealized loss position	0.00%
Governmental agency mortgage-backed securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 4,487	4,036
Governmental agency mortgage-backed securities | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 4,487
Percentage of debt securities in unrealized loss position	100.00%
Governmental agency mortgage-backed securities | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Governmental agency mortgage-backed securities | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 0
Percentage of debt securities in unrealized loss position	0.00%
U.S. corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 853	533
U.S. corporate debt securities | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 411
Percentage of debt securities in unrealized loss position	48.20%
U.S. corporate debt securities | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 327
Percentage of debt securities in unrealized loss position	38.30%
U.S. corporate debt securities | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 115
Percentage of debt securities in unrealized loss position	13.50%
Foreign corporate debt securities
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 378	$ 234
Foreign corporate debt securities | Investment Grade | A- or higher
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 169
Percentage of debt securities in unrealized loss position	44.70%
Foreign corporate debt securities | Investment Grade | BBB+ to BBB-
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 175
Percentage of debt securities in unrealized loss position	46.30%
Foreign corporate debt securities | Non-Investment Grade
Schedule Of Available For Sale Securities [Line Items]
Estimated fair value of debt securities, Unrealized loss position	$ 34
Percentage of debt securities in unrealized loss position	9.00%