Income Taxes (Details) - USD ($) $ in Millions	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Net charge included in total income tax expense related to TCJA at the date of enactment										$ 129
Current income tax expense included in consolidated statement of income, federal									$ 424		$ 899
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									41	56	21
Current income tax expense included in consolidated statement of income, state									8	4	8
Total current tax expense									473	395	928
Deferred income tax expense included in consolidated statement of income, federal									(13)	337	110
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									(22)	(58)	1
Total deferred tax expense (benefit)									(35)	279	111
Total income tax expense included in the consolidated statement of income	$ 125	$ 97	$ 107	$ 109	$ 309	$ 27	$ 195	$ 143	438	674	1,039
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)									(349)	110	(289)
Total income tax expense included in the consolidated financial statements									$ 89	$ 784	$ 750