Pension Plans, Retirement Benefits and Savings Plans (details) - Fair Value (USD $) In Millions, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	$ 3,357	$ 3,203	$ 2,859
Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	16	17	18
Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2,552	2,543
Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	803	656
Level 2 [Member] | Postretirement Benefit Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	16	17
Level 3 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2	4
Fixed maturities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	524	490
Fixed maturities [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	524	490
Obligations of states, municipalities and political subdivisions [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	19	18
Obligations of states, municipalities and political subdivisions [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	19	18
Debt securities issued by foreign governments [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	17	14
Debt securities issued by foreign governments [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	17	14
Mortgage-backed securities, collateralized mortgage obligations and pass-through securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	14	11
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	14	11
All other corporate bonds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	474	447
All other corporate bonds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	474	447
Total mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,900	1,801
Total mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,890	1,801
Total mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	10
Equity mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,290	1,355
Equity mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	1,283	1,355
Equity mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	7
Bond mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	610	446
Bond mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	607	446
Bond mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	3
Equity securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	616	571
Equity securities [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	615	570
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	4
Other investments [Member] | Level 3 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	2	4	6
Cash and short-term securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	315	337
Cash and short-term securities [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	47	172
Cash and short-term securities [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	268	165
Cash and short-term securities, U.S. Treasury securities [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets		122
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		122
Money market mutual funds [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	22	19
Money market mutual funds [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	18	19
Money market mutual funds [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	4
Cash and short-term securities, other [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	293	196
Cash and short-term securities, other [Member] | Level 1 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	29	31
Cash and short-term securities, other [Member] | Level 2 [Member] | Pension Plans [Member]
Defined benefit plan disclosure
Fair value of plan assets	$ 264	$ 165