Investments (details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Investments disclosure
Fixed maturities, due in one year or less, amortized cost	$ 6,240
Fixed maturities, due after 1 year through 5 years, amortized cost	16,741
Fixed maturities, due after 5 years through 10 years, amortized cost	16,008
Fixed maturities, due after 10 years, amortized cost	18,026
Fixed maturities excluding mortgage-backed securities, collateralized mortgage obligations and pass-through securities, amortized cost	57,015
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities, amortized cost	1,863
Fixed maturities, amortized cost	58,878	$ 60,801
Fixed maturities, due in one year or less, fair value	6,324
Fixed maturities, due after 1 year through 5 years, fair value	17,296
Fixed maturities, due after 5 years through 10 years, fair value	16,260
Fixed maturities, due after 10 years, fair value	18,797
Fixed maturities excluding mortgage-backed securities, collateralized mortgage obligations and pass-through securities, fair value	58,677
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities, fair value	1,981
Fixed maturities, at fair value	60,658	63,474
Securities on loan as part of a tri-party lending agreement	269	296
Proceeds from sales of fixed maturities classified as available for sale	1,950	1,049	$ 1,635
Insurance subsidiaries' securities on deposit at financial institutions in certain states pursuant to the respective states' insurance regulatory requirements	4,660	4,780
Fair value of funds deposited with third parties to be used as collateral to secure various liabilities on behalf of insureds, cedants and other creditors	28	39
Fair value of other investments pledged as collateral securing outstanding letters of credit	21	22
Fair value of owned securities held by an insurance subsidiary pledged into a Lloyd's trust account to support capital requirements for the Company's operations at Lloyd's	140	151
Proceeds from sales of equity securities	59	158	86
Proceeds from sale of real estate investments	31	15	$ 18
Real estate held for sale	0	0
Accumulated depreciation on real estate held for investment purposes	320	290
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2016	92
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2017	74
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2018	61
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2019	49
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2020	36
Future minimum rental income expected on operating leases relating to the Company's real estate properties for 2021 and thereafter	$ 59
Maximum original maturity of short-term securities	1 year
Combined average days to maturity of short-term securities (in days)	67 days
Amortized cost of short-term securities (which approximates fair value)	$ 4,670	$ 4,360