Segment Information - Segment Information (Details) $ in Millions	3 Months Ended			6 Months Ended		9 Months Ended
	Jun. 30, 2020 USD ($)	Dec. 31, 2019 segment	Jun. 30, 2019 USD ($)	Jun. 30, 2020 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2019 segment
Segment Reporting Information [Line Items]
Number of reportable segments | segment		2				1
Revenue, ancluding adjustments	$ 294		$ 263	$ 484	$ 497
Total revenues	294		263	484	497
Total expenses	150		85	296	223
Income (loss) before income taxes and equity in net earnings of investees	144		178	188	274
Equity in net earnings of investees	0		1	(4)	3
Adjusted operating income (loss) before income taxes	144		179	184	277
Provision (benefit) for income taxes	20		38	30	50
Less: Noncontrolling interests	5		0	2	0
Adjusted Income (Loss) Attributable to Parent	119		141	152	227
Net investment income	78		110	158	208
Interest expense	21		22	43	45
Non-cash compensation and operating expenses	15		11	30	23
Corporate, Non-Segment [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	0		1	(4)	1
Total revenues	0		1	(4)	1
Total expenses	32		31	67	62
Income (loss) before income taxes and equity in net earnings of investees	(32)		(30)	(71)	(61)
Equity in net earnings of investees	0		0	(5)	1
Adjusted operating income (loss) before income taxes	(32)		(30)	(76)	(60)
Provision (benefit) for income taxes	(6)		(4)	(11)	(9)
Less: Noncontrolling interests	0		0	0	0
Adjusted Income (Loss) Attributable to Parent	(26)		(26)	(65)	(51)
Net investment income	0		1	1	2
Interest expense	23		22	48	46
Non-cash compensation and operating expenses	0		2	3	3
Segment Reconciling Items [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	38		21	23	22
Total revenues	35		21	16	21
Total expenses	4		14	3	14
Income (loss) before income taxes and equity in net earnings of investees	31		7	13	7
Equity in net earnings of investees	(26)		0	(16)	0
Adjusted operating income (loss) before income taxes	5		7	(3)	7
Provision (benefit) for income taxes	0		1	(1)	1
Less: Noncontrolling interests	5		0	2	0
Adjusted Income (Loss) Attributable to Parent	0		6	(4)	6
Net investment income	(4)		(1)	(8)	(3)
Interest expense	(2)		0	(5)	(1)
Non-cash compensation and operating expenses	0		0	0	0
Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	(3)		0	(7)	(1)
Insurance Segment [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	244		241	437	474
Total revenues	246		241	442	475
Total expenses	90		40	174	147
Income (loss) before income taxes and equity in net earnings of investees	156		201	268	328
Equity in net earnings of investees	26		1	17	2
Adjusted operating income (loss) before income taxes	182		202	285	330
Provision (benefit) for income taxes	28		41	46	58
Less: Noncontrolling interests	0		0	0	0
Adjusted Income (Loss) Attributable to Parent	154		161	239	272
Net investment income	82		110	165	209
Interest expense	0		0	0	0
Non-cash compensation and operating expenses	9		9	18	20
Insurance Segment [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	2		0	5	1
Asset Management [Member] | Operating Segments [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	12		0	28	0
Total revenues	13		0	30	0
Total expenses	24		0	52	0
Income (loss) before income taxes and equity in net earnings of investees	(11)		0	(22)	0
Equity in net earnings of investees	0		0	0	0
Adjusted operating income (loss) before income taxes	(11)		0	(22)	0
Provision (benefit) for income taxes	(2)		0	(4)	0
Less: Noncontrolling interests	0		0	0	0
Adjusted Income (Loss) Attributable to Parent	(9)		0	(18)	0
Net investment income	0		0	0	0
Interest expense	0		0	0	0
Non-cash compensation and operating expenses	6		0	9	$ 0
Asset Management [Member] | Intersegment Eliminations [Member]
Segment Reporting Information [Line Items]
Revenue, ancluding adjustments	$ 1		$ 0	$ 2