Investments Investments - Bank loans amortized cost by credit quality and year of acquisition (Details) - USD ($) $ in Millions	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available for Sale Securities
Amortized cost, net	$ 4,759	$ 4,817
Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	1,196
Allowance	(79)
Amortized cost, net	1,117
2015 and prior | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	52
2016 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	82
2017 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	248
2018 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	378
2019 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	320
Current | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	116
BBB | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	41
BBB | 2015 and prior | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	0
BBB | 2016 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	0
BBB | 2017 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	10
BBB | 2018 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	18
BBB | 2019 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	9
BBB | Current | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	4
BB | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	236
BB | 2015 and prior | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	31
BB | 2016 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	4
BB | 2017 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	43
BB | 2018 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	70
BB | 2019 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	67
BB | Current | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	21
B | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	711
B | 2015 and prior | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	12
B | 2016 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	38
B | 2017 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	155
B | 2018 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	237
B | 2019 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	185
B | Current | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	84
CCC and below | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	208
CCC and below | 2015 and prior | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	9
CCC and below | 2016 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	40
CCC and below | 2017 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	40
CCC and below | 2018 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	53
CCC and below | 2019 | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	59
CCC and below | Current | Bank loans, net
Schedule of Available for Sale Securities
Amortized cost before allowance	$ 7