Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Current income tax expense included in consolidated statement of income, federal									$ 546	$ 424
Current income tax expense included in consolidated statement of income, federal (excluding impact of TCJA)											$ 314
Current income tax expense included in consolidated statement of income, impact of TCJA at enactment											21
Current income tax expense included in consolidated statement of income, foreign									7	41	56
Current income tax expense included in consolidated statement of income, state									6	8	4
Total current tax expense									559	473	395
Deferred income tax expense included in consolidated statement of income, federal									(33)	(13)	337
Deferred income tax expense included in consolidated statement of income, federal (excluding impact of TCJA)											229
Deferred income tax expense included in consolidated statement of income, impact of TCJA at enactment											108
Deferred income tax expense included in consolidated statement of income, foreign									(10)	(22)	(58)
Total deferred tax expense (benefit)									(43)	(35)	279
Total income tax expense included in the consolidated statement of income	$ 201	$ 36	$ 108	$ 171	$ 125	$ 97	$ 107	$ 109	516	438	674
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)									641	(349)	110
Total income tax expense included in the consolidated financial statements									$ 1,157	$ 89	$ 784