Investments Investments - Off balance sheet collateral from reverse repurchase agreements (Details) - USD ($) $ in Millions	Sep. 30, 2020	Dec. 31, 2019
Offsetting Assets [Line Items]
Securities Purchased under Agreements to Resell	$ 0	$ 190
Securities Purchased under Agreements to Resell, Fair Value of Collateral	$ 0	$ (630)

Amount, after the effects of master netting arrangements, of funds outstanding loaned in the form of a security resale agreement between the entity and another party for the purchase and resale of identical or substantially the same securities at a date certain for a specified price. Includes purchases of participations in pools of securities that are subject to a resale agreement, assets not subject to a master netting arrangement and not elected to be offset.

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Name:	us-gaap_SecuritiesPurchasedUnderAgreementsToResell
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant