Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Income Tax Disclosure [Abstract]
Current income tax expense included in consolidated statement of income, federal									$ 532	$ 546	$ 424
Current income tax expense included in consolidated statement of income, foreign									35	7	41
Current income tax expense included in consolidated statement of income, state									4	6	8
Total current tax expense									571	559	473
Deferred income tax benefit included in consolidated statement of income, federal									(29)	(33)	(13)
Deferred income tax benefit included in consolidated statement of income, foreign									(2)	(10)	(22)
Total deferred tax benefit									(31)	(43)	(35)
Total income tax expense included in the consolidated statement of income	$ 306	$ 159	$ (45)	$ 120	$ 201	$ 36	$ 108	$ 171	540	516	438
Expense (benefit) relating to changes in the unrealized gain (loss) on investments, unrealized loss on foreign exchange and other items in other comprehensive income (loss)									490	641	(349)
Total income tax expense included in the consolidated financial statements									$ 1,030	$ 1,157	$ 89