Investments (Leased Real Estate Investments - Operating Leases) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	$ 4,502		$ 4,502		$ 4,132
Office
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	2,205		2,205		1,999
Operating Lease, Lease Income	42	$ 44	86	$ 89
Retail
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	1,096		1,096		1,006
Operating Lease, Lease Income	25	25	49	51
Apartment
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	256		256		253
Operating Lease, Lease Income	5	19	10	37
Industrial
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	276		276		223
Operating Lease, Lease Income	11	10	22	19
Land
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	505		505		489
Operating Lease, Lease Income	5	4	10	9
Hotel
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	95		95		94
Operating Lease, Lease Income	1	0	3	0
Other
Schedule of Operating Leases by Property Type [Line Items]
Leased real estate investments, Carrying Value	69		69		$ 68
Operating Lease, Lease Income	1	2	2	3
Leased real estate investments
Schedule of Operating Leases by Property Type [Line Items]
Operating Lease, Lease Income	$ 90	$ 104	$ 182	$ 208