Pension Plans, Retirement Benefits and Savings Plans (details) - Fair Value - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	$ 3,242	$ 3,357	$ 3,203
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	15	16	$ 17
Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2,565	2,552
Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	675	803
Level 2 [Member] | Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	15	16
Level 3 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2	2
Fixed maturities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	540	524
Fixed maturities [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	540	524
Obligations of states, municipalities and political subdivisions [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	17	19
Obligations of states, municipalities and political subdivisions [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	17	19
Debt securities issued by foreign governments [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	16	17
Debt securities issued by foreign governments [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	16	17
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	16	14
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	16	14
All other corporate bonds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	491	474
All other corporate bonds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	491	474
Total mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,886	1,900
Total mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,877	1,890
Total mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	9	10
Equity mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,237	1,290
Equity mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,231	1,283
Equity mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	6	7
Bond mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	649	610
Bond mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	646	607
Bond mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	3	3
Equity securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	625	616
Equity securities [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	624	615
Equity securities [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1	1
Other investments [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2	2
Other investments [Member] | Level 3 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2	2
Cash and short-term securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	189	315
Cash and short-term securities [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	64	47
Cash and short-term securities [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	125	268
Cash and short-term securities, U.S. Treasury securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	25
Cash and short-term securities, U.S. Treasury securities [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	25
Money market mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	23	22
Money market mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	19	18
Money market mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	4	4
Cash and short-term securities, other [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	141	293
Cash and short-term securities, other [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	20	29
Cash and short-term securities, other [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	$ 121	$ 264