Investments (Leased Real Estate Investments - Operating Leases) (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	$ 4,516		$ 4,516		$ 4,132
Office
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	2,098		2,098		1,999
Operating Lease, Lease Income	45	$ 42	131	$ 131
Retail
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	1,151		1,151		1,006
Operating Lease, Lease Income	32	21	81	72
Apartment
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	255		255		253
Operating Lease, Lease Income	6	23	16	60
Industrial
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	304		304		223
Operating Lease, Lease Income	11	10	33	29
Land
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	533		533		489
Operating Lease, Lease Income	5	5	15	14
Hotel
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	94		94		94
Operating Lease, Lease Income	2	1	5	1
Other
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	81		81		$ 68
Operating Lease, Lease Income	2	1	4	4
Leased real estate investments
Schedule of Operating Leases by Property Type [Line Items]
Operating Lease, Lease Income	$ 103	$ 103	$ 285	$ 311