Claim and Claim Adjustment Expense Reserves (Life & Group Policyholder Reserves) (Details) - USD ($) $ in Millions	3 Months Ended			12 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2020
Liability for Claims and Claims Adjustment Expense [Abstract]
Liability for unpaid claims and claims adjustment expense structured settlement obligations period increase (decrease)	$ 46
Liability for unpaid claims and claims adjustment expense, long term care policies, period increase (decrease)	37
Liability for unpaid claims and claims adjustment expense, period increase (decrease)		$ 56	$ 31
Premium deficiency and future policy benefit	$ 74	$ 216		$ 74